CN113381026B

CN113381026B - Polyimide-based flexible electrode and preparation and application thereof

Info

Publication number: CN113381026B
Application number: CN202110663182.0A
Authority: CN
Inventors: 刘龙飞; 唐智勇; 成娟娟; 欧云; 马朝勇
Original assignee: Hunan University of Science and Technology
Current assignee: Hunan University of Science and Technology
Priority date: 2021-06-15
Filing date: 2021-06-15
Publication date: 2022-07-01
Anticipated expiration: 2041-06-15
Also published as: CN113381026A

Abstract

The invention belongs to the field of flexible batteries, and particularly discloses a polyimide-based flexible electrode which comprises a polyimide substrate, an oxide active substance film and an upper coating conductive film, wherein the polyimide substrate is etched to be combined with a conductive layer. The invention also relates to a preparation method of the polyimide-based flexible electrode, which comprises the steps of carrying out pattern etching on polyimide, carrying out surface activation, then compounding a conducting layer, regulating and controlling the pyrolysis temperature of the oxide active substance film grown by spray pyrolysis and the proportion of a precursor solution, and finally selectively coating the conducting film on the surface of the active substance. Compared with conventional current collectors such as copper foils and aluminum foils, the polyimide substrate of the composite conducting layer of the polyimide-based flexible electrode prepared by the invention is lighter in weight, thinner in thickness and capable of being repeatedly bent, and has a certain flame retardant effect; the active substance film prepared by spray pyrolysis is tightly combined with the current collector, and has controllable appearance and thickness and excellent electrochemical performance.

Description

Polyimide-based flexible electrode and preparation and application thereof

Technical Field

The invention belongs to the technical field of flexible energy storage, and particularly relates to a flexible electrode of a flexible lithium secondary battery.

Background

The lithium secondary battery has the advantages of high specific energy, good cycle performance, no memory effect, environmental protection and the like, and is a high-efficiency secondary battery with the greatest development prospect and a chemical energy storage power source with the fastest development. The lithium secondary battery is composed of positive and negative electrode plates, a diaphragm, electrolyte and positive and negative electrode shells, wherein the electrode plates are generally prepared from a current collector, an active substance, a conductive agent and a binder by a coating method. The reaction mechanism of the lithium secondary battery can be classified into three types, i.e., intercalation/deintercalation, alloying/dealloying, oxidation and reduction. The lithium secondary battery may be classified into a flexible battery and a non-flexible conventional battery from the viewpoint of flexibility. With the development of scientific technology, flexible batteries have wide application in wearable electronic devices and other portable devices, and are receiving more and more attention. The inflexible conventional battery electrode manufacturing process mostly adopts coating on a current collector, then placing the current collector in a drying oven, and setting a certain temperature and a certain drying time to volatilize a solvent in slurry. The electrode prepared by the coating method has low bonding degree of active substances and a current collector, and the battery is not suitable for working under repeated bending change conditions. Generally, flexible batteries require flexibility in the electrode assembly or current collector. In the report of the flexible battery, the current collector mostly adopts carbon-based flexible material as the current collector, which makes the range of selectable materials of the current collector limited; the preparation process of the electrode active substance mainly adopts the means of spinning technology, chemical/physical vapor deposition, chemical electroplating and the like, and the preparation process flow is complex or requires a precise instrument.

Disclosure of Invention

In view of the defects of the existing flexible battery, the first object of the invention is to provide a polyimide-based flexible electrode, aiming at improving the rate performance, the cycle performance, the energy density and the stability of the flexible battery.

The second purpose of the invention is to provide the preparation method of the polyimide-based flexible electrode, and the purpose is to improve the performance of the prepared flexible battery.

A third object of the present invention is to provide the use of the polyimide-based flexible electrode in a flexible lithium secondary battery.

A fourth object of the present invention is to provide a flexible lithium secondary battery equipped with the polyimide-based flexible electrode.

A polyimide-based flexible electrode comprises a polyimide substrate and an active substance film layer which are sequentially compounded;

the polyimide substrate comprises a polyimide film, an etched pattern is arranged on the surface A of the polyimide film, a conductive film layer A is compounded on the surface A of the polyimide film, and the conductive film layer A is in contact with an active substance film layer; and a conductive film layer B is arranged on the surface B of the polyimide film.

According to the invention, the etching pattern is innovatively formed on the bottom surface of the polyimide base, and the active substance film layer and the conductive film are further compounded.

In the invention, the polyamide membrane can be directly purchased as a commercial product or manufactured by self, the thickness specification of the polyamide membrane is not required, the use requirement of the flexible electrode is met, and the thickness can be 8-125 mu m, for example.

In the present invention, the A, B sides of the polyimide film refer to the front and back surfaces of the polyimide film.

In the present invention, the B-side of the polyimide film is preferably also provided with an etching pattern. In the present invention, it is preferable that both surfaces of the polyimide are provided with the etching pattern.

Preferably, the locations of the etched patterns of the A, B planes correspond or do not correspond;

preferably, the etched patterns of the A, B planes are through or not through each other in the thickness direction. For example, the etching depth is 1 to 125 μm.

Preferably, the etching pattern is at least one of a grid pattern formed by etching lines and a lattice pattern formed by etching holes;

preferably, the planar shape of the etching hole is at least one of a triangle, a circle and a pentagram. The planar shape refers to a pattern reserved on the surface of the polyimide by etching holes.

Preferably, the etching holes are arranged independently of each other. That is, the boundaries between the etch holes are not in contact.

Preferably, the distance between adjacent etching holes is more than or equal to 1 time of the diameter of the circumcircle of the etching hole;

preferably, the diameter of the circumscribed circle of the etching hole is 40-250 μm.

Preferably, the conductive film layer a is left with a rough surface due to an etching pattern. That is, the distances between the surface of the conductive film layer a and the surface of the polyimide a at different positions are substantially the same.

Preferably, the conductive film layer B is filled in the etching pattern and has a flat or nearly flat surface.

Preferably, the materials of the conductive film layer a and the conductive film layer B are at least one of simple metal, alloy, carbon material, conductive metal compound and indium tin oxide;

preferably, the metal simple substance is at least one of copper, aluminum and nickel;

preferably, the alloy is at least one of a nickel-chromium alloy, a nickel-iron alloy, and an iron-cobalt alloy;

preferably, the carbon material is at least one of carbon black, fullerene and graphene;

preferably, the thicknesses of the conductive film layer A and the conductive film layer B are 10-1000 nm independently;

preferably, the sheet resistance of the polyimide substrate is 0.1 to 100 Ω · m.

The active material film layer contains a metal oxide of at least one of nickel, titanium, copper, manganese, cobalt, and the like.

Preferably, the active substance film layer is obtained by spray pyrolysis of the corresponding metal salt.

Preferably, the active material film layer is a nanoparticle layer or a nanofiber layer of a metal oxide.

Preferably, the active material film layer further comprises a carbon material, preferably at least one of hydroxyl carbon nanotubes and carboxyl carbon nanotubes;

preferably, the thickness of the active material film layer is 0.1 μm to 20 μm.

Preferably, the surface of the active material film layer is also compounded with a conductive film C;

preferably, the conductive film C is at least one of a conductive metal and a carbon material; preferably, the conductive metal is at least one of copper, aluminum and nickel. Preferably, the carbon material is carbon nanotubes.

Preferably, the thickness of the conductive film C is 10 to 1000 nm.

Preferably, the flexible polyimide-based flexible electrode is a pure polyamide film which is directly purchased as a commercial product and has the thickness of 4-5 mu m.The etching pattern is circular, the diameter is 50 micrometers, the distance between the upper part and the lower part of each circle and the distance between the upper part and the lower part of each circle are 40-50 micrometers, and the etching depth is the penetration film layer. The material A, B of the conductive layer is simple substance nickel, and the thickness of the nickel plating is respectively

And

the oxide in the oxide active material film is nickel oxide. The upper cladding conductive film C is copper

The invention also provides a preparation method of the polyimide-based flexible electrode, which comprises the following steps:

step (1): substrate preparation

Patterning and etching the surface A of the polyimide, then carrying out surface activation, and then compounding a conductive film layer A on the surface A of the polyimide film; a conductive film layer B is arranged on the surface B of the polyimide film;

step (2): spray pyrolysis

An active material thin film is grown on the surface of the conductive film layer A by a spray pyrolysis method.

According to the invention, the surface of the polyimide is etched innovatively, and the cooperation with the spray pyrolysis process is further realized, so that the cooperation can be generated, the stability of the prepared flexible electrode can be effectively improved, and the rate capability, the cycle performance, the energy density and the cycle stability of the electrode can be improved.

In the invention, the combined cooperation of the patterning etching and spray pyrolysis process is a key for improving the performance of the flexible battery, for example, the rate performance, the cycle performance and the energy density of the flexible battery can be effectively improved through the cooperation of the processes; the key points of improving the stability of the lithium battery, effectively preventing the thermal runaway of the battery and improving the safety performance of the lithium battery are provided.

Preferably, the polyimide is patterned by cold laser etching.

Preferably, the micropattern etch process is processed using a picosecond ultraviolet laser cutter. The parameters of the patterning etching can be adjusted according to the use requirement.

Preferably, in step (1), the B-side of the polyimide is also subjected to pattern etching.

In the invention, the film thickness penetrating patterning etching can be directly carried out on one surface in consideration of the convenience of operation and use, and compared with the non-penetrating etching, the polyimide current collector of the penetrating etching composite conductive layer does not need to be additionally led out with a tab in the subsequent use.

Preferably, the plasma treatment is used to activate the surface and change the adhesion of the film. Compared with a chemical activation treatment method, the plasma treatment method has the advantages that the time required by the plasma treatment is short, harmful chemical reagents can be avoided, and a cleaning object is dried after being cleaned by the plasma and can be sent to the next procedure without being dried. For example, the PI film after pattern etching may be immersed in deionized water to perform ultrasonic cleaning, and then dried in a forced air drying oven, and then activated by setting certain parameter conditions in an oxygen atmosphere with a plasma cleaning machine.

Preferably, the plasma equipment adopts a Dongxin Kogaku plasma cleaning machine, and the specific parameters of the plasma cleaning are as follows: the vacuum degree is-100 KPa, the cleaning time is 3-5min, the used atmosphere is high-purity oxygen, the gas flow is 100-800 mL/min, and the power is 600-800W.

Preferably, the conductive film layers a and B are formed on the surface of the polyimide film by at least one of physical transfer, coating, electroplating, and vacuum evaporation;

preferably, the conductive film layers a and B are formed on the surface of the polyimide film by vacuum evaporation.

In the present invention, the current and conditions of the vacuum coating process can be adjusted based on the existing mechanism.

Preferably, the current in the vacuum coating process is 10-40A; the vacuum evaporation rate is preferably

In the invention, better coating conditions can be further selected according to the difference of coating elements. For example, the nickel plating current is 30-35A; the copper plating current is 22-26A; the aluminum plating current is 16-20A.

In the present invention, an active layer can be formed on the surface of the conductive layer a by a conventional spray pyrolysis method. Researches show that under the process system, the metal concentration and the pyrolysis temperature in the spraying process are further controlled in a combined manner, so that the synergy is further improved, and the electrochemical performance of the prepared material is improved.

Preferably, pyrolyzing a precursor homogeneous solution of a metal source for forming an active substance film at the temperature of 300-400 ℃, and then annealing for 4-8h to form the active substance film; in the precursor homogeneous phase solution, the concentration of the metal source is 0.1-1 mol/L.

According to the invention, under the innovation of the patterned etching, the spray pyrolysis and the control of the temperature and the homogeneous solution concentration in the treatment process are matched, so that the stability of the flexible battery and the performance of the assembled flexible battery can be further improved in a synergistic manner.

Preferably, the metal source is an inorganic or organic salt of at least one metal of nickel, titanium, copper, manganese, cobalt, etc.;

preferably, the inorganic salt is at least one of chloride, nitrate and acetate of corresponding metal;

preferably, the organic salt is an acetylacetonate salt of the respective metal. The present inventors have surprisingly found that with this metal source, it is possible to match the control of the conditions described, to unexpectedly form an active film layer in the form of oxide fibres, which surprisingly has better properties.

In the precursor homogeneous phase solution, the solvent of the metal inorganic salt is a mixed solution of deionized water and absolute ethyl alcohol, and the solvent of the metal organic salt solution is a mixed solution of acetonitrile and absolute ethyl alcohol.

Preferably, in the solvent of the two metal salts, in order to obtain better metal salt solubility and subsequent spray pyrolysis effect, the volume ratio of the absolute ethyl alcohol is 40-60%.

Preferably, in order to improve the problems of metal oxide conductivity, active material volume expansion in electrochemical reaction and the like, a carbon material is also added into the precursor homogeneous solution.

Preferably, the carbon material added into the precursor homogeneous phase solution is at least one of hydroxyl carbon nanotube and carboxyl carbon nanotube, and the adding proportion is 0.01-0.05 g/L; more preferably 0.03 to 0.05 g/L. In the invention, the carbon material is added into the spraying solution, and the concentration control of the carbon material is further matched, so that the carbon material is beneficial to further cooperating with the process, and the electrochemical performance is further improved.

Preferably, the spray pyrolysis means may employ air compression spraying, ultrasonic electrostatically-assisted spraying, or the like.

Preferably, the polyimide substrate of the composite conductive layer is subjected to a heat pretreatment, for example, a preliminary temperature rise to 350 ℃.

Preferably, the temperature of the spray pyrolysis is 350-400 ℃.

Preferably, further comprising step (3): and coating a conductive film C on the surface of the active substance film to obtain the flexible electrode.

Preferably, the conductive film layer C is formed on the surface of the active material film layer by any one of physical transfer, coating means, electroplating, and vacuum evaporation. The material selection and the preparation method of the conductive film layer C are the same as those of the conductive film layer A or B.

The polyimide-based flexible electrode manufactured by the method has the advantages of wide applicable active substances, high purity of the active substances and controllable appearance. The preparation method of the polyimide-based flexible electrode comprises the following specific operation steps:

and S1, pattern etching treatment is carried out on the front side and the back side of the polyimide.

S2, the S1 polyimide composite conducting layer. In step S2, the etched polyimide film needs to be pretreated before the composite conductive layer is formed, including ultrasonic cleaning, drying, roughening, and grafting oxygen-containing functional groups. Wherein, the grafting oxygen-containing functional group can adopt plasma cleaning, chemical means and the like under oxygen atmosphere. The polyimide composite conductive layer is formed by combining a conductive material and a polyimide film by one or more methods of physical transfer, coating means, electroplating, chemical vapor deposition, vacuum evaporation, magnetron sputtering, atomic layer deposition, electron beam deposition and the like.

S3, the S2 conductive polyimide is sprayed with a pyrolytic growth active substance. The high-temperature-resistant pattern etching conductive polyimide film can be subjected to spray pyrolysis operation of a metal salt solution at the temperature of 300-400 ℃. The pretreatment temperature of the high temperature resistant patterned conductive polyimide film is determined by the pyrolysis temperature of the metal salt solution. The metal salt solution is divided into metal organic salt solution (such as acetylacetone metal salt) and metal inorganic salt solution (such as metal nitrate and metal chloride), and the concentration of the metal salt solution is properly configured according to the requirement (generally 0.1-1 mol/L). The metal salt solution can be doped with a conductive material according to the conductivity of the spray pyrolysis active substance.

S4, if necessary, a conductive film (conductive film C) may be coated on the surface of the S3 active material film. The upper coating conductive film can be compounded by one or more methods such as physical transfer, coating means, electroplating, chemical vapor deposition, vacuum evaporation, magnetron sputtering, atomic layer deposition, electron beam deposition and the like.

The invention also provides application of the polyimide-based flexible electrode in preparation of a flexible lithium secondary battery.

The present invention also provides a flexible lithium secondary battery equipped with the polyimide-based flexible electrode.

Has the advantages that:

1. compared with conventional current collectors such as copper foils and aluminum foils, the polyimide-based flexible electrode with a brand-new structure is lighter in weight, thinner in thickness and capable of being repeatedly bent, and the polyimide-based conductive current collector has a certain flame-retardant effect based on the inherent characteristics of polyimide. Moreover, the flexible electrode is assembled into a battery, and can show better electrochemical performance;

2. the invention also provides a patterned etching-spray pyrolysis synergistic process, the prepared active substance film is tightly combined with the current collector, the appearance of the active substance can be controlled by solution proportion, spray particle size and the like, and the reproducibility degree is high.

Based on the two points, the battery prepared by the invention can improve the rate capability, the cycle performance and the energy density of the battery; meanwhile, the stability of the lithium battery can be improved, and the thermal runaway of the lithium battery can be effectively prevented, so that the safety performance of the lithium battery is improved.

Drawings

Fig. 1 is a schematic diagram of a polyimide-based flexible electrode.

FIG. 2 shows the cold laser etching aperture of pure polyimide film by percutaneous second ultraviolet laser cutting machine

And the subsequent photomicrograph.

FIG. 3 is a graph showing the comparison of the resistance of the polyimide film of the composite nickel conductive layer after etching, the nickel foil and the pure polyimide film.

Figure 4 shows a graph of polyimide film flexibility for a composite nickel conductive layer.

FIG. 5 scanning electron micrograph of a polyimide film of the composite nickel conductive layer (conductive layer B).

Fig. 6 is a scanning electron microscope image of the polyimide-based current collector of the composite nickel conductive layer, which is formed by spray pyrolysis of a nickel chloride salt solution to form a nickel oxide film.

Fig. 7 is a graph of the cycle characteristics and coulombic efficiency of example 1.

Fig. 8 implementation case 2 cycle characteristics and coulombic efficiency plots.

Fig. 9 is a flow chart for preparing the polyimide-based flexible electrode.

Fig. 10 embodiment 3 cycle characteristics and coulombic efficiency chart.

FIG. 11 is a comparison graph of Nyquist plots for example 1, example 2 and example 3.

Fig. 12 is a scanning electron microscope image of a polyimide-based current collector spray pyrolysis nickel acetylacetonate solution of the composite nickel conductive layer to generate a nickel oxide film.

Fig. 13 is a graph of the cycle characteristics and coulombic efficiency for example 4.

Fig. 14 is a graph of cycle characteristics and coulombic efficiency for example 5.

Fig. 15 is a graph of the cycle characteristics and coulombic efficiency for example 6.

FIG. 16 is a comparative graph of the laser etching of the embodiment 1 and the comparative example 1.

Figure 17 is a graph comparing the cycle characteristics and coulombic efficiency of example 2.

Fig. 18 is a comparison graph of nyquist plots of embodiment 1, comparative embodiment 2 and embodiment 4.

FIG. 19 is a comparison graph of cycle characteristics of the precursor solutions with concentrations of 0.1mol/L, 0.5mol/L, 1mol/L, and 2.5mol/L, respectively.

FIG. 20 is a XRD contrast diagram of pyrolysis temperatures at 250 deg.C, 300 deg.C, and 350 deg.C.

FIG. 21 shows the charge transfer resistances R at concentrations of 0.01g/L, 0.03g/L, 0.05g/L, 0.1g/L, and 0.3g/L, respectively_CTAnd (5) a variation graph.

FIG. 22 is a comparison graph of cycle characteristics at concentrations of 0.01g/L, 0.03g/L, 0.1g/L, 0.2g/L, and 0.3g/L for the hydroxy carbon nanotubes.

Detailed Description

In order to facilitate the intuitive understanding of the present invention, the following description of the preferred embodiments of the present invention is provided in terms of preferred combinations. It is to be noted that the combination of the invention and its embodiments and steps are not limited to the specific embodiments described below. Indeed, these embodiments are provided so that the reader will be more fully and thoroughly understood the relevant disclosure of the invention. The invention is subject to modifications, variations and alterations by those skilled in the art, which are still inherent in the invention, and which are still within the scope of the invention.

Example 1:

and etching the polyimide film pattern. The pure polyamide film with length and width of 70 x 100mm was cut to a thickness of 5 μm. The pattern was drawn in the form of circles with a diameter of 50 μm and a pitch of 50 μm between adjacent circles. And importing the graphic file, setting parameters such as output power, pulse width, focal length and the like of the picosecond ultraviolet laser cutting machine, enabling the polyimide film to be positioned at a proper position of a workbench of the laser etching machine, and then etching, wherein the etching depth is penetration. And placing the etched polyimide film in a water tank filled with deionized water for ultrasonic cleaning, repeatedly washing with the deionized water for 3-5 times, and then placing the polyimide film in a constant-temperature drying oven at 40-50 ℃ for drying for 6-8 hours. Placing the dried etched polyimide film in a plasma cleaning machine for treatment, wherein the specific parameters are as follows: the vacuum degree is-100 KPa, the cleaning time is 3min, the used atmosphere is high-purity oxygen, the gas flow is 150mL/min, and the power is 600W.

And (5) conducting treatment of the polyimide film. The plasma-treated polyimide film was laid flat and fixed on a mask plate of a vacuum evaporator, and the film was fed into a vacuum evaporation chamber and mounted, followed by copper plating, nickel plating or aluminum plating (in this case, nickel plating).

Copper plating: and (4) placing the copper metal particles in a tungsten basket of a vacuum evaporation machine, and closing the cabin door. Manual vacuum pumping: and opening a vacuum gauge, sequentially opening the mechanical pump and the pre-pumping valve, closing the pre-pumping valve after the resistance specification number is below 5Pa, sequentially opening the front-stage valve and the molecular pump, and opening the gate valve to perform deep vacuum pumping after the screen of the molecular pump displays the rotating speed. When the ionization gauge number reaches 8 x 10^-4After Pa or less, vacuum deposition was started. Vacuum evaporation: opening the film thickness meter, opening the corresponding evaporation boat and the probe baffle of the film thickness meter, rotating the current knob to slowly increase the current (24A), observing the evaporation rate in the film thickness meter, and when the evaporation rate is stabilized at

At this time, the substrate shutter is opened to perform vapor deposition of a copper film (conductive film layer A). When the film thickness gauge reading reaches the required thickness

The substrate shutter is immediately closed. The other side (conductive film layer B) of the polyimide film was subjected to the same plating treatment as in the previous evaporation step to give a film thickness

Nickel plating: except for the difference of partial parameters, other specific operations and related parameters are consistent with the copper plating operation, and the different parameters are as follows: the current knob is rotated to slowly ramp up the current to 32A.

Aluminum plating: except for the difference of partial parameters, other specific operations and related parameters are consistent with the copper plating operation, and the different parameters are as follows: the current knob is rotated to slowly ramp up the current to 18A.

Spray pyrolysis of the active. Preparing 0.5mol/L nickel chloride salt solution: weighing absolute ethyl alcohol, deionized water and nickel chloride hexahydrate, and mixing according to a certain amount, wherein the absolute ethyl alcohol and the deionized water have equal volume. And then placing the solution bottle on a DF-101S heat collection type constant temperature heating magnetic stirrer for constant temperature magnetic stirring, wherein the temperature is 30-35 ℃, and the stirring time is 1 h. Placing the polyimide film (nickel-plated and with the conductive film layer A facing upwards) etched with the conductive micropattern on a temperature-controlled pyrolysis table to perform constant-temperature heating pretreatment, wherein the temperature is 350 ℃, setting a program of the temperature-controlled pyrolysis table for 1h to raise the temperature from room temperature to a target temperature, then keeping the temperature for 8h, and finally lowering the temperature from 350 ℃ to 30 ℃ for 4 h. And sucking the prepared salt solution by using a liquid-transfering gun, injecting the salt solution into the spray gun, and then setting a spray gun valve at a proper position for spray pyrolysis. The spraying is required to be uniform, and a certain amount of solution is sprayed at intervals of 3-5 s per 1mL so that the film thickness is about 2000 nm.

And (5) loading the battery and performing battery data test. The button cell case specification is CR2025, the prepared electrode is a positive electrode, the lithium sheet is a negative electrode, the diaphragm is a polypropylene film (the active layer of the positive electrode and the negative electrode are separated by the diaphragm), and the electrolyte is LiPF₆And (3) solution. Constant-current cyclic charge and discharge tests are carried out on a Xinwei battery test system, the charge and discharge voltage is set to be 0-3V, and the multiplying power is set to be 0.1C. Impedance test is carried out by adopting a Chenghua electrochemical workstation, the frequency is from 100KHz to 0.1Hz, and the amplitude is 5 mV.

The later microscopic picture shows that the etched aperture size and the circular hole gap of the same specification are almost equalIn line, the deviation of the actual etching aperture from the set aperture value is within the error range of the equipment.

Fig. 3 is a graph comparing the resistance of the polyimide film of the etched composite nickel conductive layer with the resistance of the nickel foil and the resistance of the pure polyimide film, and it can be seen that the difference between the resistance of the polyimide film of the etched composite nickel conductive layer and the resistance of the nickel foil is small.

Fig. 5 is a scanning electron micrograph of a polyimide film of the composite nickel conductive layer (conductive layer B). It can be seen from the figure that the pure polyimide film is covered by dense nickel atoms and the morphology is flat.

Fig. 6 is a scanning electron microscope image of a polyimide-based current collector of the composite nickel conductive layer spray-pyrolyzed with a nickel chloride salt solution to form a nickel oxide film.

Fig. 7 is a graph of the cycle characteristics and coulombic efficiency for example 1.

As can be seen from the figure, the 50 th charging and discharging specific capacities are 168.79mAh/g, 172.02mAh/g and the charging and discharging efficiency is 98.13%. Comparing with comparative example 2, it can be seen that the electrochemical performance is slightly higher than that of the conventional coating without the doped hydroxyl carbon nanotube and the coated conductive film.

Example 2:

compared with embodiment 1, the main difference is that the oxide layer is added with hydroxyl carbon nanotubes.

The polyimide film of the composite conductive layers (a and B) was selected from those nickel-plated in example 1.

Spray pyrolysis of the active. Preparing 0.5mol/L nickel oxide salt solution: anhydrous ethanol, deionized water and nickel chloride hexahydrate are weighed and mixed according to a certain amount, wherein the volume of the anhydrous ethanol and the deionized water is equal, and then 0.03g/L of hydroxyl carbon nano tube is added. And then placing the solution bottle on a DF-101S heat collection type constant temperature heating magnetic stirrer for constant temperature magnetic stirring, wherein the temperature is 30-35 ℃, and the stirring time is 1 h. Then, the solution bottle is subjected to ultrasonic treatment, so that the hydroxyl carbon nanotube is dispersed more uniformly, and the specific parameters are as follows: the ultrasonic time is more than or equal to 30min, the ultrasonic power is 480W, and the temperature is controlled at 30-35 ℃. Placing the polyimide film (plated with copper) etched with the conductive micropattern on a temperature-controlled pyrolysis table to perform constant-temperature heating pretreatment, wherein the temperature is 350 ℃, setting a program of the temperature-controlled pyrolysis table for 1h to raise the temperature from room temperature to a target temperature, then keeping the temperature for 8h, and finally lowering the temperature from 350 ℃ to 30 ℃ for 4 h. And sucking the prepared salt solution by using a liquid-transfering gun, injecting the salt solution into the spray gun, and then setting a spray gun valve at a proper position for spray pyrolysis. The spraying is required to be uniform, and every 1mL of the solution is sprayed for 3-5 s, so that the film thickness is about 2000 nm.

The subsequent pretreatment and spray pyrolysis procedures were the same as those of example 1.

The battery was charged and the battery data test operation was performed as in example 1.

Fig. 8 embodiment 2 cycle characteristics and coulombic efficiency chart.

As can be seen from the figure, the 50 th charging and discharging specific capacities are 401.19mAh/g, 429.3mAh/g and the charging and discharging efficiency is 93.45%. Compared with the embodiment 1, the electrochemical performance of the carbon nanotube is obviously improved under the condition of doping the hydroxyl carbon nanotube of 0.03 g/L. The addition of the carbon nanotubes not only can improve the conductivity, but also can intercalate/deintercalate lithium ions to provide partial capacity.

Example 3:

compared with the embodiment 2, the main difference is that the surface of the active layer is further compounded with a copper conducting layer;

mainly comprises the following steps: the polyimide film of the composite conductive layers (a and B) was selected to be nickel-plated as in example 2.

The precursor solution formulation and related operating procedures for spray pyrolysis of the active were the same as in example 2.

And conducting film coating treatment is carried out on the surface of the active material.

And carrying out vacuum copper film evaporation coating treatment on the active substance surface subjected to spray pyrolysis. The specific steps and parameters are as follows: the film compounded with the active substance is spread and fixed on a mask plate of a vacuum evaporation plating machine and is sent into a vacuum evaporation plating chamber for installation. And (4) placing the copper metal particles in a tungsten basket of a vacuum plating machine, and closing the cabin door. Manual vacuum pumping: opening the vacuum gauge, sequentially opening the mechanical pump and the pre-pumping valve, and electricallyAnd after the resistance indication number is below 5Pa, closing the pre-pumping valve, sequentially opening the front-stage valve and the molecular pump, and opening the gate valve to perform deep vacuum pumping after the screen of the molecular pump displays the rotating speed. When the ionization gauge reaches 8 x 10^-4After Pa or less, vacuum deposition was started. Vacuum evaporation: opening the film thickness meter, opening the corresponding evaporation boat and the probe baffle of the film thickness meter, rotating the current knob to slowly increase the current (24A), observing the evaporation rate in the film thickness meter, and when the evaporation rate is stabilized at

At the same time, the substrate baffle is opened to carry out the evaporation plating of the copper film (conductive film layer C). When the film thickness gauge reading reaches the required thickness

The substrate shutter is immediately closed.

Fig. 9 is a flow chart for preparing the polyimide-based flexible electrode.

The numbers in the figures refer to the following, respectively: 1 (conductive layer B), 2 (polyimide film), 3 (conductive layer a), 4 (active material layer), and 5 (coating conductive film layer C).

Fig. 10 implementation case 3 cycle characteristics and coulombic efficiency plots.

As can be seen from the figure, the 50 th charging and discharging specific capacities are 520.12mAh/g, 539.75mAh/g and the charging and discharging efficiency is 96.36 percent respectively. Compared with the embodiment 2, it can be seen that the electrochemical performance of the doped 0.03g/L hydroxyl carbon nanotube is obviously improved under the condition of conducting film coating. The cladding of the copper conductive film helps to connect the unconnected carbon nanotube conductive network.

Fig. 11 is a comparison graph of nyquist plots of embodiment 1, embodiment 2, and embodiment 3.

It can be seen from the figure that the charge transfer resistances decrease in order, with corresponding values of 1300 Ω, 800 Ω, and 600 Ω, respectively.

Example 4:

compared with the example 1, the difference is mainly that the spray pyrolysis process of the active layer is different, mainly the difference of the types of metal sources is as follows:

the polyimide film of the composite conductive layers (a and B) was selected to be nickel-plated as in example 1.

Spray pyrolysis of the active. Preparing 0.5mol/L nickel acetylacetonate salt solution: weighing absolute ethyl alcohol, acetonitrile and nickel acetylacetonate, and mixing according to a certain quantity, wherein the absolute ethyl alcohol and the acetonitrile have equal volume. The subsequent pretreatment and spray pyrolysis procedures were the same as those of example 1.

Comparing fig. 6, it can be seen that the morphology of the active material film produced is different due to the difference in the metal salt solution.

As can be seen from the figure, the 50 th charging and discharging specific capacities are 181.06mAh/g, 181.90mAh/g and the charging and discharging efficiency is 99.54%. Compared with the embodiment 1, the electrochemical performance is better.

Example 5:

compared with the embodiment 4, the main difference is that the hydroxyl carbon nano-tubes are added in the oxide layer.

The polyimide film of the composite conductive layer was selected to be nickel-plated as in example 1.

Spray pyrolysis of the active. Preparing 0.5mol/L nickel acetylacetonate salt solution: anhydrous ethanol, acetonitrile and nickel acetylacetonate are weighed and mixed according to a certain quantity, wherein the volume of the anhydrous ethanol is equal to that of the acetonitrile, the volume of the anhydrous ethanol is equal to that of the deionized water, and then 0.03g/L of hydroxyl carbon nano-tubes are added. The subsequent pretreatment and spray pyrolysis procedures were the same as those of example 2.

As can be seen from the figure, the 36 th charging and discharging specific capacities are 520.06mAh/g, 551.65mAh/g and the charging and discharging efficiency is 94.27%.

Example 6:

the polyimide film of the composite conductive layer was selected from those plated with nickel in example 1.

The precursor solution formulation and related procedures for spray pyrolysis of the active were the same as in example 5.

And conducting film coating treatment is carried out on the surface of the active material. The steps and parameters of the vacuum vapor plating copper film coating treatment on the active material surface after spray pyrolysis are consistent with those of embodiment 3.

As can be seen from the figure, the specific capacity of the 30 th charging and discharging is 519.78mAh/g, 532.68mAh/g and the charging and discharging efficiency is 97.58%. It can be seen from comparative example 5 that the cycle performance after coating the conductive film is more stable.

Comparative example 1:

and etching the polyimide film pattern. The pure polyamide film with length and width of 70 x 100mm was cut to a thickness of 5 μm. The pattern was drawn in the form of circles with a diameter of 50 μm and a pitch of 25 μm between adjacent circles. And importing the graphic file, setting parameters such as output power, pulse width, focal length and the like of the picosecond ultraviolet laser cutting machine, enabling the polyimide film to be positioned at a proper position of a workbench of the laser etching machine, and then etching, wherein the etching depth is penetration.

Since the distance between the upper and lower parts and the left and right parts of the adjacent etched circles is less than 1 time of the diameter of the circumscribed circle of the etching hole, the etched film is partially collapsed (as shown in FIG. 16) and cannot be used for subsequent operations.

FIG. 16 is a comparison between the laser etching of example 1 and comparative example 1.

In the figure, D1 represents comparative example 1, and S1 represents example 1. It is apparent from the figure that the partial area of the etched figure of comparative example 1 is collapsed to cause unevenness.

Comparative example 2:

the main difference compared to example 1 is that the nickel active layer is formed by coating, instead of the spray pyrolysis described:

And (4) coating by a conventional method. Preparing nickel oxide coating slurry, wherein the material proportion in the slurry is as follows: acetylene black: LA133 ═ 8: 1:1, and the solvent is a certain amount of deionized water. The treated conductive polyimide film was fixed to a coater and subjected to coating treatment. The coated sample was dried in a forced air drying oven.

As can be seen from the figure, the 50 th charging and discharging specific capacities are 142.42mAh/g, 146.69mAh/g and the charging and discharging efficiency is 97.09 percent respectively.

It can be seen from the figure that the charge transfer resistances are 1300 Ω, 1500 Ω, and 1200 Ω in this order.

Example 7:

concentration study of spray pyrolyzed metal source solutions:

The concentrations of the precursor solutions of the spray pyrolysis active substances were 0.1mol/L, 1mol/L, and 2.5mol/L, respectively, and the remaining operations and parameters were consistent with those of example 1.

It can be seen from the figure that the precursor concentration is 0.1-1 mol/L, the good performance can be shown, and the cycle characteristic is the worst at 2.5 mol/L.

Example 8:

temperature study of spray pyrolysis:

The operation and parameters of the spray pyrolysis active material were the same as those of example 1 except that the pyrolysis temperature was set to 250 ℃ and 300 ℃, respectively.

It can be seen from the figure that as the pyrolysis temperature is gradually increased, the NiO phase diffraction peak is continuously enhanced, and the width is gradually narrowed, which shows that the grain size of the synthesized product is gradually increased, and the crystallinity gradually approaches to perfect. The degree of crystallinity is weak, so that more ion diffusion and charge transmission can be generated on corresponding electrodes, and the movement of a large amount of ions can cause violent collision, so that the resistance value of charge transfer can be increased, and the electrochemical performance is influenced.

Example 9:

compared with the example 2, the difference lies in that the content of the hydroxyl carbon nanotube is researched, and the main points are as follows:

Preparing 0.5mol/L nickel oxide salt solution: anhydrous ethanol, deionized water and nickel chloride hexahydrate are weighed and mixed according to a certain amount, wherein the volume of the anhydrous ethanol and the deionized water is equal, and then 0.01g/L, 0.03g/L, 0.05g/L, 0.1g/L and 0.3g/L of hydroxyl carbon nano tubes are respectively added. And then placing the solution bottle on a DF-101S heat collection type constant temperature heating magnetic stirrer for constant temperature magnetic stirring, wherein the temperature is 30-35 ℃, and the stirring time is 1 h. Then, the solution bottle is subjected to ultrasonic treatment, so that the hydroxyl carbon nanotube is dispersed more uniformly, and the specific parameters are as follows: the ultrasonic time is more than or equal to 30min, the ultrasonic power is 480W, and the temperature is controlled at 30-35 ℃.

FIG. 21 shows the charge transfer resistances R at concentrations of 0.01g/L, 0.03g/L, 0.05g/L, 0.1g/L, and 0.3g/L, respectively_CTAnd (5) a change graph.

It can be seen from the figure that the charge transfer resistance is the smallest when the hydroxyl carbon nanotube is added at a concentration of 0.01-0.05g/L, especially 0.03g/L, and the concentration is not controlled within the range, but is not favorable for the performance.

FIG. 22 is a graph showing comparison of cycle characteristics at concentrations of 0.01g/L, 0.03g/L, 0.1g/L, 0.2g/L and 0.3g/L for hydroxy carbon nanotubes.

Claims

1. A polyimide-based flexible electrode is characterized by comprising a polyimide substrate and an active substance film layer which are sequentially compounded;

the polyimide substrate comprises a polyimide film, an etched pattern is arranged on the surface A of the polyimide film, a conductive film layer A is compounded on the surface A of the polyimide film, and the conductive film layer A is in contact with an active substance film layer; a conductive film layer B is arranged on the surface B of the polyimide film;

the preparation method of the polyimide-based flexible electrode comprises the following steps:

step (1): substrate preparation

step (2): spray pyrolysis

2. The polyimide-based flexible electrode according to claim 1, wherein the side B of the polyimide film is also provided with an etched pattern.

3. The polyimide-based flexible electrode of claim 2, wherein the A, B face etched pattern locations correspond or do not correspond.

4. The polyimide-based flexible electrode of claim 3, wherein the A, B face etched patterns are either interpenetrated or not interpenetrated in the thickness direction.

5. The polyimide-based flexible electrode according to any one of claims 1 to 4, wherein the etching pattern is at least one of a grid pattern consisting of etching lines and a lattice pattern consisting of etching holes.

6. The polyimide-based flexible electrode according to claim 5, wherein the planar shape of the etching holes is at least one of a triangle, a circle, and a pentagram.

7. The polyimide-based flexible electrode according to claim 6, wherein the etching holes are provided independently of each other.

8. The polyimide-based flexible electrode of claim 7, wherein the distance between adjacent etch holes is greater than or equal to 1 times the diameter of the circumscribed circle of the etch hole.

9. The polyimide-based flexible electrode according to claim 7, wherein the diameter of a circumscribed circle of the etching hole is 40 to 250 μm.

10. The polyimide-based flexible electrode according to claim 1, wherein the conductive film layer a leaves a rough surface due to an etching pattern.

11. The polyimide-based flexible electrode of claim 10, wherein the conductive film layer B fills the etched pattern and presents a flat or nearly flat surface.

12. The polyimide-based flexible electrode according to claim 1, wherein the active material film layer comprises a metal oxide of at least one of nickel, titanium, copper, manganese, and cobalt.

13. The polyimide-based flexible electrode of claim 12, wherein the active material film layer is obtained by spray pyrolysis of the corresponding metal salt.

14. The polyimide-based flexible electrode of claim 12, wherein the active material film layer is a nanoparticle layer or a nanofiber layer of a metal oxide.

15. The polyimide-based flexible electrode of claim 12, wherein the active material film layer further comprises a carbon material.

16. The polyimide-based flexible electrode according to claim 15, wherein the carbon material is at least one of a hydroxy carbon nanotube and a carboxy carbon nanotube.

17. The polyimide-based flexible electrode of claim 15, wherein the active material film layer is 0.1 μm to 20 μm.

18. The polyimide-based flexible electrode according to claim 1, wherein the conductive film layer A and the conductive film layer B are made of at least one of a simple metal, an alloy, a carbon material, a conductive metal compound and indium tin oxide.

19. The polyimide-based flexible electrode of claim 18, wherein the elemental metal is at least one of copper, aluminum, and nickel.

20. The polyimide-based flexible electrode of claim 18, wherein the alloy is at least one of a nickel-chromium alloy, a nickel-iron alloy, and an iron-cobalt alloy.

21. The polyimide-based flexible electrode of claim 18, wherein the carbon material is at least one of carbon black, fullerene, and graphene.

22. The polyimide-based flexible electrode of any one of claims 1 and 18 to 21, wherein the thickness of the conductive film layer a and the conductive film layer B is independently 10 to 1000 nm.

23. The polyimide-based flexible electrode according to claim 1, wherein the square resistance of the polyimide substrate is 0.1 to 100 Ω -m.

24. The polyimide-based flexible electrode according to claim 1, wherein a conductive film C is further compounded on the surface of the active material film layer.

25. The polyimide-based flexible electrode according to claim 24, wherein the conductive film C is at least one of a conductive metal and a carbon material; the conductive metal is at least one of copper, aluminum and nickel; the carbon material is a carbon nanotube.

26. The polyimide-based flexible electrode of claim 24, wherein the conductive film C has a thickness of 10 to 1000 nm.

27. The polyimide-based flexible electrode according to claim 1, wherein in step (1), the polyimide is also pattern etched on side B.

28. The polyimide-based flexible electrode of claim 27, wherein the patterned etch is performed using a cold laser etch.

29. The polyimide-based flexible electrode of claim 1, wherein the surface activation is performed by plasma cleaning.

30. The polyimide-based flexible electrode according to claim 1, wherein the conductive film layers a and B are formed on the surface of the polyimide film by at least one of physical transfer, coating, electroplating, and vacuum evaporation.

31. The polyimide-based flexible electrode of claim 30, wherein the conductive film layers a and B are formed on the surface of the polyimide film by vacuum evaporation.

32. The polyimide-based flexible electrode of claim 31, wherein the current in the vacuum coating process is 10 to 40A; the vacuum evaporation rate is 0.1-0.2A/s.

33. The polyimide-based flexible electrode according to claim 1, wherein a precursor homogeneous solution of a metal source for forming the active material film layer is pyrolyzed at a temperature of 300 to 400 ℃ and then annealed for 4 to 8 hours to form the active material film layer; in the precursor homogeneous phase solution, the concentration of the metal source is 0.1-1 mol/L.

34. The polyimide-based flexible electrode of claim 33, wherein the metal source is an inorganic or organic salt of at least one metal selected from the group consisting of nickel, titanium, copper, manganese, and cobalt.

35. The polyimide-based flexible electrode of claim 34, wherein the inorganic salt is at least one of chloride, nitrate, and acetate of the corresponding metal.

36. The polyimide-based flexible electrode of claim 35, wherein the organic salt is an acetylacetonate salt of the respective metal.

37. The polyimide-based flexible electrode of claim 33, wherein in the precursor homogeneous solution, the solvent of the metal inorganic salt is a mixed solution of deionized water and absolute ethyl alcohol, and the solvent of the metal organic salt solution is a mixed solution of acetonitrile and absolute ethyl alcohol.

38. The polyimide-based flexible electrode of claim 37, wherein the anhydrous ethanol is present in a ratio of 40% to 60% in the solvent for the two metal salts.

39. The polyimide-based flexible electrode of claim 37, wherein a carbon material is further added to the precursor homogeneous solution.

40. The polyimide-based flexible electrode of claim 39, wherein the carbon material added to the precursor homogeneous solution is at least one of hydroxyl carbon nanotubes and carboxyl carbon nanotubes, and the addition ratio is 0.01-0.05 g/L.

41. The polyimide-based flexible electrode according to claim 1, further comprising step (3): and coating a conductive film C on the surface of the active substance film layer to obtain the flexible electrode.

42. The polyimide-based flexible electrode of claim 41, wherein the conductive film layer C is formed on the surface of the active material film layer by any one of physical transfer, coating, electroplating and vacuum evaporation.

43. Use of a polyimide-based flexible electrode according to any one of claims 1 to 42 in the preparation of a flexible lithium secondary battery.

44. A flexible lithium secondary battery equipped with the polyimide-based flexible electrode according to any one of claims 1 to 42.