In-situ microporous polymer membrane, preparation method and application thereof

Abstract

The application discloses an in-situ microporous polymer film, a preparation method and application thereof. The polymer film is uniformly distributed with controllable size penetrating micropores, which is coated on the surface of an object to play an insulation protection role and meanwhile allows components in the object to exchange with media through the film material. In the preparation method, a film forming agent solution is coated on the object to be protected, the object is immersed into a second solvent after the solution is evaporated and concentrated, and the residual solvent is separated and extracted, so that the microporous film is formed. By adjusting the evaporation and concentration conditions and proportion of the film forming agent on the surface of the object, the porosity and pore size of the microporous film can be achieved. Compared with traditional film materials, the in-situ microporous film is simple to make, low in preparation cost and use cost, and has a cost performance advantage. The in-situ microporous polymer film is suitable for being used as a diaphragm between positive and negative electrodes of a rechargeable ion battery and a protective film of a detection electrode.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of materials, and particularly relates to an in-situ microporous polymer membrane, a preparation method and application thereof. BACKGROUND

[0002] The microporous polymer membrane has wide application in the fields of industry, medicine, pesticide, etc., and can be used as a filter membrane and a slow-release controlled-release membrane. The separator between the positive electrode and the negative electrode of a lithium ion battery is also a microporous polymer membrane, which mainly separates the positive electrode and the negative electrode of the battery to prevent the short circuit caused by the contact of the two electrodes, and the micropores on the membrane material allow the ions in the electrolyte to pass freely.

[0003] At present, most of the microporous membrane materials are manufactured and used separately. For example, the separator of the lithium ion battery is independent of the positive electrode and the negative electrode of the battery and is arranged between the positive electrode and the negative electrode. The separate separator increases the manufacturing and using cost and also increases the volume and weight of the battery.

[0004] Therefore, in view of the problems existing in the current separator materials of metal ion batteries and the common problems existing in the application of microporous membranes in other fields, a comprehensive solution is needed. SUMMARY

[0005] The purpose of the present application is to solve the problems of poor universality and high cost of the lithium ion battery separator and the similar common problems existing in the application of microporous membranes in other fields, and a solution is provided, i.e. an in-situ microporous polymer membrane, a preparation method and application thereof.

[0006] The technical scheme adopted by the present application is as follows:

[0007] In a first aspect, the present application provides an in-situ microporous polymer membrane, which is a polymer membrane formed by coating a polymer on the surface of an object in-situ, and the polymer membrane uniformly distributes through-penetrating micropores with controllable size.

[0008] As a preferred embodiment of the first aspect, the polymer is a high-molecular polymer that can be dissolved in an organic solvent, including but not limited to polystyrene (PS), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC) and polyacrylonitrile (PAN).

[0009] As a preferred embodiment of the first aspect, the object includes but is not limited to the electrode of a secondary battery and a solid-state detection electrode, which needs to exchange substances with the environment through water or other media during use.

[0010] In a second aspect, the present application provides a preparation method of the in-situ microporous polymer membrane, and the steps are as follows:

[0011] 1) adding the polymer powder into the first solvent, stirring until completely dissolved to obtain a polymer solution with a concentration of 3% to 8%;

[0012] 2) uniformly coating the polymer solution on the surface of the target object in need of insulation protection, and then placing the target object into an oven, keeping the temperature at 0.3T1 to 0.6T1 for 10 to 20 minutes, so as to partially evaporate the first solvent and form a polymer semi-cured film with micropores on the surface of the target object in situ; T1 is the boiling point of the first solvent in Celsius; the first solvent is an organic solvent with a boiling point higher than 120°C, and the solubility of the polymer in the first solvent is not less than 8%; the first solvent is wet to the surface of the target object but has no solubility, corrosivity and chemical reactivity to the target object;

[0013] 3) immersing the target object coated with the polymer semi-cured film into the second solvent for 10 to 30 minutes to extract the residual first solvent in the film, and then evaporating the second solvent to form a polymer film with micropores on the surface of the target object in situ; T2 is the boiling point of the second solvent in Celsius; the second solvent is an organic solvent with a boiling point lower than the softening point of the polymer or water, and the second solvent is miscible with the first solvent in an infinite proportion and has no solubility, corrosivity and chemical reactivity to the polymer and the target object.

[0014] As a preferred embodiment of the second aspect, the first solvent includes dimethylbenzene (DMB), N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO) or triethyl phosphate (TEP).

[0015] As a preferred embodiment of the second aspect, the second solvent includes methanol, ethanol, acetone or dimethyl carbonate (DMC).

[0016] As a preferred embodiment of the second aspect, the polymer is a high-molecular polymer that can be dissolved in an organic solvent, including polystyrene (PS), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC) or polyacrylonitrile (PAN).

[0017] In a third aspect, the present application provides a coated electrode, which takes the electrode body as the target object, and the surface of the electrode body is coated with a polymer film with micropores in situ by the preparation method according to any one of the second aspect.

[0018] As a preferred embodiment of the third aspect, the electrode is a solid-state detection electrode, and the polymer film coated on the surface is used to slow down the corrosion of harmful components in the medium to be detected to the electrode.

[0019] As a preferred embodiment of the third aspect, the solid-state detecting electrode is a solid-state ion-selective electrode used in electrochemical sensors, including but not limited to Ag / AgCl electrode and Ag / Ag2S electrode.

[0020] As a preferred embodiment of the third aspect, the coated electrode is used as a positive electrode or a negative electrode of a secondary battery, and the polymer film coated on the surface of the electrode is used to replace the separator between the positive electrode and the negative electrode in the battery.

[0021] In a fourth aspect, the present application provides a secondary battery, which comprises an electrolyte liquid, and a positive electrode and a negative electrode used in pairs and immersed in the electrolyte liquid, wherein the part of the positive electrode or the negative electrode in contact with the electrolyte liquid is coated with a microporous polymer film in situ by the preparation method of any one of the second aspect.

[0022] As a preferred embodiment of the fourth aspect, the positive electrode of the secondary battery is an electrode pressed from lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium iron phosphate (LFP), lithium nickel cobalt manganese oxide (NCM), or lithium nickel cobalt aluminum oxide (NCA); the negative electrode of the secondary battery is an electrode pressed from graphitized carbon material, natural graphite, or anatase intercalated graphite; and the electrolyte liquid is an electrolyte solution consistent with the cations contained in the positive electrode.

[0023] As a preferred embodiment of the fourth aspect, a metal foil or a metal wire is implanted in the positive electrode and the negative electrode pressed, as a conductor for connecting an external circuit. Preferably, the shape and thickness of the positive electrode and the negative electrode are substantially consistent.

[0024] The polymer is a high-molecular polymer that can be dissolved in an organic solvent, including but not limited to polystyrene (PS), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), and polyacrylonitrile (PAN).

[0025] Compared with the prior art, the present application has the following advantages:

[0026] The present application provides an in-situ microporous polymer film, and a preparation and use method of the separator. Compared with conventional film materials, the in-situ microporous film preparation technology is mature, the process is simple, the preparation cost and use cost are low, and the in-situ microporous polymer film has a cost-effective advantage. The in-situ microporous polymer film is suitable for use as a separator between positive and negative electrodes of a rechargeable ion battery, and a protective film of a detecting electrode. DETAILED DESCRIPTION

[0027] The present application will be further described and illustrated with reference to specific embodiments.

[0028] The first aspect of the present application provides an in-situ microporous polymer film, which is a polymer film formed by in-situ coating of a polymer on the surface of an object, and the polymer film uniformly distributes controllable penetrating micropores.

[0029] The present application directly precipitates the microporous film on the surface of an object, which can effectively reduce the preparation and use cost. Compared with the commonly used split film material, the in-situ microporous film has advantages in preparation and use cost.

[0030] The polymer mentioned in the present application is a high molecular polymer that can be dissolved in an organic solvent, including but not limited to polystyrene (PS), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyacrylonitrile (PAN), etc.

[0031] The selection of the type of polymer not only needs to consider the use environment, such as environmental temperature and medium composition, but also needs to consider the matching between the film material and the coated object, such as surface affinity and adhesion.

[0032] For the sake of description, the coated object that needs to be insulated is called target object. The target object mentioned in the present application includes but is not limited to the electrode of a secondary battery and a solid-state detection electrode, which needs to exchange substances with the environment through water or other media during use.

[0033] The in-situ microporous polymer film of the present application is one of the most economically valuable application scenarios for replacing the current lithium ion battery separator. The in-situ microporous polymer film is a thin film formed by in-situ cross-linking precipitation of a polymer solution on the surface, and structural micropores are formed during film formation, so that lithium ions can pass through during charging and discharging reactions, and insulation is achieved. When using the electrode with the in-situ microporous polymer film to assemble a battery, a separator is no longer needed between the positive electrode and the negative electrode, which simplifies the manufacturing process, saves the comprehensive cost, and reduces the volume and weight of the battery.

[0034] In other occasions where slow-release and controlled-release technology is needed, the in-situ microporous polymer film has the same technical advantages and cost-effective advantages compared with the traditional split separator.

[0035] The second aspect of the present application provides a preparation method of the in-situ microporous polymer film, which can achieve the purpose of microporous film porosity and pore size by adjusting the evaporation concentration conditions and proportion of the film forming agent on the surface of the object. The steps are as follows:

[0036] 1) Add the polymer powder into the first solvent, stir until completely dissolved, and obtain a polymer solution with a concentration of 3% to 8%.

[0037] The first step of the above method for preparing the in-situ microporous polymer film is to prepare a solution of the polymer powder to be used for preparing the microporous film, thereby obtaining a film-forming agent solution. The polymer is a high-molecular polymer that can be dissolved in an organic solvent, including but not limited to polystyrene (PS), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyacrylonitrile (PAN), etc.

[0038] The first solvent used in the present application is an organic solvent with a boiling point T1 higher than 120°C, in which the solubility of the polymer is not less than 8%, and which has wetting properties for the surface of the target object under the microporous polymer film but does not have solubility, corrosiveness or chemical reactivity for the target object, including but not limited to dimethylbenzene (DMB), N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), and triethyl phosphate (TEP).

[0039] The selection of the polymer powder and the first solvent is primarily based on the matching of their solubility, i.e. the polymer used should be able to dissolve in the solvent and have a sufficiently high solubility. Secondly, the compatibility and matching between the prepared solution and the object to be coated should be considered, including the wetting properties and surface affinity of the solution for the surface of the target object, which is a prerequisite for the film-forming agent solution to uniformly coat the object. If the wetting properties and surface affinity between the film-forming agent solution and the object to be coated are insufficient, surface modification of the surface of the object to be coated or the addition of a surfactant to the film-forming agent solution is required. Surface modification and the use of surfactants involve well-known general techniques and will not be described here.

[0040] The concentration of the polymer powder in the film-forming agent solution is related to the thickness of the film and can be adjusted as needed. The use of a high-boiling organic solvent as the first solvent for preparing the film-forming agent solution can slow down the evaporation rate of the solvent, which is beneficial to the control of the evaporation process of the solvent.

[0041] 2) The polymer solution is uniformly coated on the surface of the target object that needs to be insulated and protected, and then the target object is placed in an oven, and the temperature is kept at 0.3T1~0.6T1 for 10 to 20 minutes, so that the first solvent is partially evaporated, thereby forming a microporous polymer semi-cured film on the surface of the target object. The above-mentioned parameter T1 is the boiling point of the first solvent in degrees Celsius.

[0042] The second step of the above-mentioned in-situ microporous polymer film preparation method is to coat the film-forming agent solution on the surface of the object and evaporate part of the solvent under controllable conditions (30% to 60% of the boiling point of the first solvent) to form a semi-cured film. During the heating and evaporation process, the concentration of the film-forming agent causes the polymer to precipitate and form a network structure, and the residual solution is contained in the semi-cured polymer network. By adjusting the temperature of the oven and the time of the object coated with the film-forming agent solution in the oven, the evaporation ratio of the solution in the film-forming agent during the semi-curing stage can be controlled, thereby achieving the purpose of controlling the porosity and pore size of the microporous film. Lower ambient temperature and shorter constant temperature time result in less precipitated polymer, higher porosity and larger pore size of the initial film; higher ambient temperature and longer constant temperature time result in more precipitated polymer, lower porosity and smaller pore size of the initial film.

[0043] The target object of the present application includes but is not limited to the electrodes of secondary batteries and solid-state detection electrodes, which need to exchange materials with the environment through water or other media during use.

[0044] 3) The target object coated with the semi-cured polymer film is immersed in the second solvent for 10 to 30 minutes to extract the residual first solvent in the film, and after being taken out, the second solvent is evaporated in an environment with a temperature of 0.5T2 to 0.8T2, forming an in-situ microporous polymer film on the surface of the object. The above-mentioned parameter T2 is the boiling point of the second solvent in Celsius.

[0045] The third step of the above-mentioned in-situ microporous polymer film preparation method is to remove the residual first solvent in the initial film through the selective dissolution of the second solvent to the first solvent, i.e. extraction, so that the porosity and pore structure of the initial film are completely preserved. When the target object coated with the semi-cured initial film is immersed in the second solvent, the first solvent in the residual solution of the initial film is extracted by the second solvent, and the solute in the residual solution, i.e. the polymer network precipitated in the evaporation stage in the previous step, is preserved completely, thus preserving the pore structure.

[0046] The second solvent of the present application is an organic solvent or water with a boiling point lower than the softening point of the polymer, which can be infinitely miscible with the first solvent, and has no solubility, corrosion and chemical reactivity to the polymer and the target object under the in-situ microporous polymer film, including but not limited to methanol, ethanol, acetone, dimethyl carbonate (DMC).

[0047] The third aspect of the present application provides several use scenarios of the in-situ microporous polymer film, including:

[0048] 1) According to the preparation method provided in the above-mentioned second aspect, the in-situ microporous polymer film is coated on the positive electrode or negative electrode of a secondary battery, replacing the separator between the positive electrode and the negative electrode.

[0049] Therefore, based on this use scenario, the present application can design a secondary battery, which contains an electrolyte liquid, and a battery positive electrode and a battery negative electrode used in pairs and immersed in the electrolyte liquid, wherein the part of the battery positive electrode or the battery negative electrode in contact with the electrolyte liquid is coated with a microporous polymer film in situ by the preparation method of the second aspect.

[0050] The secondary battery positive electrode, the negative electrode and the electrolyte liquid of the present application need to be selected according to actual needs. Among them, the secondary battery positive electrode is preferably a sheet or plate-shaped body pressed from lithium cobaltate (LCO), lithium manganate (LMO), lithium ferrophosphite (LFP), lithium nickel cobalt manganate (NCM), lithium nickel cobalt aluminum (NCA), and a metal foil or wire is implanted inside as a conductor for connecting the external circuit. The battery negative electrode of the present application is preferably an electrode pressed from graphitized carbon material, natural graphite, or anatase intercalated graphite, which has a shape and thickness basically consistent with the battery positive electrode.

[0051] In actual use of the secondary battery of the present application, only one of the battery positive electrode or the negative electrode is coated with a microporous polymer film in situ by the method provided by the present application, which can replace the separator between the battery positive electrode and the negative electrode.

[0052] The electrolyte liquid used in the battery needs to be consistent with the cations contained in the battery positive electrode, and can be one of lithium ion electrolyte solution, magnesium ion electrolyte solution, and aluminum ion electrolyte solution. It is recommended to use commercial products, or to prepare them according to the formula of commercial products. The technology involved is a commonly known general technology.

[0053] Under normal circumstances, only one of the positive electrode or the negative electrode of the same battery needs to be coated, which can achieve the purpose of insulation and ion permeation, thereby replacing the separator arranged between the positive electrode and the negative electrode.

[0054] The separator between the positive electrode and the negative electrode of the secondary battery has an insulating effect on the one hand, to prevent short circuiting of the positive electrode and the negative electrode inside the battery, and on the other hand, to allow ion permeation during the charge and discharge reaction, so that the charge and discharge reaction can proceed. The most typical representative is various separators used in lithium ion batteries. These separators are independent of the electrodes of the battery, and the manufacturing and use are relatively high. If the in-situ microporous polymer film of the present application is used to replace the separate separator, the cost of the lithium ion battery will be significantly reduced, and the energy density per unit volume and weight of the battery will be improved by reducing the volume and weight of the separator.

[0055] 2) The in-situ microporous polymer film is coated on the surface of the solid-state detection electrode according to the preparation method of the second aspect, to slow down the corrosion of harmful components in the medium to be tested on the electrode, and prolong the service life of the electrode.

[0056] The solid-state detecting electrode as described in the present application is a solid-state ion selective electrode used in electrochemical sensors, including but not limited to Ag / AgCl electrode and Ag / Ag2S electrode.

[0057] According to the preparation method of the second aspect, the in-situ microporous polymer film is coated on the surface of the solid-state detecting electrode to slow down the corrosion of harmful components in the medium to be measured on the electrode, thereby prolonging the service life of the electrode. The in-situ microporous polymer film provided by the present application is suitable for coating a solid-state electrode, especially an ion-sensitive film detecting electrode made of inorganic material, such as Ag / AgCl electrode and Ag / Ag2S electrode.

[0058] The solid-state detecting electrode is a detecting element of an electrochemical sensor. When such a sensor is used to observe the ecological environment parameters of water for a long time, the sensitive film on the surface of the detecting electrode will be corroded by chemical components in the water, and thus the electrode will fail soon after use. For example, the AgCl film on the surface of Ag / AgCl electrode will be corroded by carbonate and sulfide ions, and the silver sulfide film on the surface of Ag / Ag2S electrode will be oxidized. Coating the electrode with a hydrophobic in-situ microporous polymer film can effectively slow down the corrosion of the electrode and prolong the service life of the electrode.

[0059] Of course, the above-mentioned several scenarios are not the only use scenarios of the in-situ microporous polymer film of the present application. Such an in-situ microporous polymer film can be applied to any coated electrode. By taking the electrode body as the target object, the preparation method of the second aspect can be used to coat the electrode body with a microporous polymer film in-situ on the part of the surface of the electrode body that needs to exchange matter with the environment through water or other medium, thereby improving the stability and service life of the electrode.

[0060] The above use scenarios of the present application will be described in detail below with reference to the embodiments.

[0061] Embodiment 1

[0062] 1) Polyvinylidene fluoride (PVDF) powder was added to dimethylacetamide (DMAC), and the mixture was stirred until the PVDF powder was completely dissolved to obtain a solution with a concentration of 3%.

[0063] 2) The polyvinylidene fluoride solution was uniformly coated on the surface of a lithium iron phosphate (LFP) plate-shaped battery anode, and then the battery anode was placed in an oven for constant temperature at 60°C for 20 minutes to evaporate part of the DMAC, thereby forming an in-situ microporous PVDF semi-cured film on the surface of the battery anode.

[0064] 3) The battery anode coated with the semi-cured film was immersed in dimethyl carbonate (DMC) for 30 minutes, and then taken out and dried in an oven at 60°C to evaporate the DMC, thereby forming an in-situ microporous PVDF film on the surface of the battery anode.

[0065] Embodiment 2

[0066] 1) Polyacrylonitrile (PAN) powder was added to dimethylformamide (DMF) and stirred until completely dissolved to obtain a solution with a concentration of 8%.

[0067] 2) The polyacrylonitrile solution was uniformly coated on the surface of a battery anode pressed from anatase intercalated graphite, and then the battery anode was placed in an oven, and was kept at a constant temperature of 60°C for 10 minutes, so that part of the DMF evaporated, forming an in-situ microporous PAN semi-cured film on the surface of the battery anode.

[0068] 3) The battery anode coated with the semi-cured film was immersed in methanol for 30 minutes, and after being taken out, the methanol was air-dried at room temperature, forming an in-situ microporous PAN film on the surface of the battery anode.

[0069] Example 3

[0070] 1) Polyvinylidene fluoride (PVDF) powder was added to N-methyl pyrrolidone (NMP) and stirred until completely dissolved to obtain a solution with a concentration of 5%.

[0071] 2) The polyvinylidene fluoride solution was uniformly coated on the surface of a plate-shaped battery cathode pressed from lithium nickel cobalt manganese oxide (NCM), and then the battery cathode was placed in an oven, and was kept at a constant temperature of 100°C for 20 minutes, so that part of the NMP evaporated, forming an in-situ microporous PVDF semi-cured film on the surface of the battery cathode.

[0072] 3) The battery cathode coated with the semi-cured film was immersed in dimethyl carbonate (DMC) for 10 minutes, and after being taken out, the DMC was evaporated in an oven at 50°C, forming an in-situ microporous PVDF film on the surface of the battery cathode.

[0073] Example 4

[0074] 1) Polyvinyl chloride (PVC) powder was added to dimethylacetamide (DMAC) and stirred until completely dissolved to obtain a solution with a concentration of 5%.

[0075] 2) The polymer solution was uniformly coated on the surface of a plate-shaped battery cathode pressed from lithium nickel cobalt aluminum oxide (NCA), and then the battery cathode was placed in an oven, and was kept at a constant temperature of 80°C for 10 minutes, so that part of the DMAC evaporated, forming an in-situ microporous PVC semi-cured film on the surface of the battery cathode.

[0076] 3) The object coated with the semi-cured film was immersed in ethyl methyl carbonate (EMC) for 20 minutes, and after being taken out, the EMC was evaporated in an oven at 50°C, forming an in-situ microporous PVC film on the surface of the battery cathode.

[0077] Example 5

[0078] 1) Polystyrene (PS) powder was added to dimethylbenzene (DMB) and stirred until completely dissolved to obtain a solution with a concentration of 6%.

[0079] 2) The polymer solution was uniformly coated on the surface of the Ag / AgCl electrode, and then the object was placed in a 50°C oven for 10 minutes to allow the DMB to partially evaporate, forming an in-situ microporous PS semi-cured film on the surface of the electrode.

[0080] 3) The Ag / AgCl electrode coated with the semi-cured film was immersed in ethanol for 10 minutes, and after being taken out, the ethanol was evaporated in a 60°C oven, forming an in-situ microporous polystyrene (PS) film on the Ag / AgCl electrode.

[0081] Example 6

[0082] 1) Polystyrene (PS) powder was added to dimethylbenzene (DMB) and stirred until completely dissolved to obtain a solution with a concentration of 6%.

[0083] 2) The polymer solution was uniformly coated on the surface of the Ag / AgCl electrode, and then the object was placed in a 50°C oven for 10 minutes to allow the DMB to partially evaporate, forming an in-situ microporous PS semi-cured film on the surface of the electrode.

[0084] 3) The Ag / AgCl electrode coated with the semi-cured film was immersed in ethanol for 10 minutes, and after being taken out, the ethanol was evaporated in a 60°C oven, forming an in-situ microporous polystyrene (PS) film on the Ag / AgCl electrode.

[0085] The above-described examples are only a preferred embodiment of the present application, and are not intended to limit the present application. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application. Therefore, any technical solutions obtained by equivalent replacement or equivalent transformation fall within the scope of the present application.

Claims

1. A method for the preparation of a microporous polymer membrane in situ, characterized in that The steps are as follows: 1) Add the polymer powder into the first solvent, and stir until completely dissolved to obtain a polymer solution with a concentration of 3% to 8%; 2) Uniformly coat the polymer solution on the surface of the target object that needs to be insulated, and then place the target object in an oven, and keep the temperature at 0.3T1~0.6T1 for 10 to 20 minutes, so that the first solvent is partially evaporated, thereby forming a polymer semi-cured film with micropores on the surface of the target object in situ; T1 is the boiling point of the first solvent in degrees Celsius; the first solvent is an organic solvent with a boiling point higher than 120°C, the solubility of the polymer in the first solvent is not less than 8%, the first solvent has wetting property on the surface of the target object but has no solubility, corrosivity and chemical reactivity to the target object; 3) Immersing the target object coated with the polymer semi-cured film into the second solvent for 10 to 30 minutes to extract the residual first solvent in the film, and then evaporate the second solvent to dryness at a temperature of 0.5T2~0.8T2, thereby forming a polymer film with micropores on the surface of the target object in situ; T2 is the boiling point of the second solvent in degrees Celsius; the second solvent is an organic solvent or water with a boiling point lower than the softening point of the polymer, and it is miscible with the first solvent in an infinite proportion, and has no solubility, corrosivity and chemical reactivity to the polymer and the target object.

2. The production method according to claim 1, wherein The first solvent includes dimethylbenzene (DMB), N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO) or triethyl phosphate (TEP).

3. The production method according to claim 1, wherein The second solvent includes methanol, ethanol, acetone or dimethyl carbonate (DMC).

4. The production method according to claim 1, wherein The polymer is a high molecular polymer that can be dissolved in an organic solvent, including polystyrene (PS), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC) or polyacrylonitrile (PAN).

5. An electrode with a coating, characterized in that The electrode body is used as the target object, and the surface of the electrode body that needs to exchange materials with the environment through water or other media is coated with a polymer film with micropores in situ by the preparation method of any one of claims 1 to 4.

6. The coated electrode of claim 5, wherein the coating is a mixture of the first and second coating materials. The coated electrode is a solid-state detection electrode, and the polymer film coated on the surface is used to slow down the corrosion of harmful components in the medium to be detected on the electrode.

7. The coated electrode of claim 6 wherein the coating is a mixture of the first and second coating materials. The solid-state detection electrode is a solid-state ion-selective electrode used on an electrochemical sensor, including but not limited to Ag / AgCl electrode and Ag / Ag2S electrode.

8. The coated electrode of claim 5 wherein, The coated electrode is used as the positive electrode or negative electrode of a secondary battery, and the polymer film coated on the surface of the electrode is used to replace the separator between the positive electrode and the negative electrode in the battery.

9. A secondary battery characterized by comprising: The battery contains an electrolyte liquid and a battery positive electrode and a battery negative electrode used in pairs and immersed in the electrolyte liquid, wherein the part of the battery positive electrode or the battery negative electrode that contacts the electrolyte liquid is coated with a polymer film with micropores in situ by the preparation method of any one of claims 1 to 4, and no independent separator is arranged between the positive electrode and the negative electrode in the battery.

10. The secondary battery according to claim 9, wherein The positive electrode of the secondary battery is an electrode made of lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium iron phosphate (LFP), lithium nickel cobalt manganese oxide (NCM), or lithium nickel cobalt aluminum oxide (NCA); the negative electrode of the secondary battery is an electrode made of graphitized carbon material, natural graphite, or anatase intercalated graphite; and the electrolyte liquid is an electrolyte solution that is consistent with the cations contained in the positive electrode.