Novel polyimide-based composite diaphragm for inhibiting growth of lithium dendrites through dual mechanisms, preparation method and lithium battery

Abstract

The invention discloses a novel polyimide-based composite diaphragm for inhibiting the growth of lithium dendrites by double mechanisms and a preparation method thereof, and the composite diaphragm is formed by coating one side or two sides of a porous membrane with a novel polyimide microsphere composition for inhibiting the growth of lithium dendrites by double mechanisms and then drying, the coating mode is one of micro-concave coating, extrusion coating, transfer type coating, dip coating or bar coating; the composition is composed of polyimide composite microspheres, a binder, a surfactant, a dispersant and an organic solvent. The novel polyimide microsphere capable of inhibiting the growth of the lithium dendrites through the dual mechanisms is provided with a polydopamine protective layer, and silver ions and magnesium ions are loaded on the surface of the polyimide microsphere. The composite diaphragm has the characteristics of high temperature resistance, high porosity, good chemical stability and high-temperature dimensional stability and the like, and the wettability of an electrolyte is improved; when the composite diaphragm is applied to the lithium battery, the growth of lithium dendrites can be remarkably inhibited, the cycling stability of the lithium battery is improved, and the service life of the lithium battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and particularly relates to a novel polyimide-based composite separator with a dual mechanism for inhibiting lithium dendrite growth, a preparation method thereof, and a lithium battery. Background Art

[0002] Since lithium batteries were commercialized, they have been widely used in fields such as portable electronic devices and electric vehicles due to their high energy density and long cycle life. However, under conditions such as high-rate charging, overcharging, or low temperature, lithium ions may precipitate on the surface of the negative electrode, forming lithium dendrites. These dendrites can pierce the separator, resulting in internal short circuits and thermal runaway in the battery, affecting the safety and life of the battery. Lithium metal batteries are considered an ideal choice for the next generation of high-energy-density lithium batteries due to their high theoretical capacity (3860 mAh / g) and low potential. However, since lithium metal batteries directly use metallic lithium as the negative electrode, the problem of dendrite growth is more prominent, leading to a decrease in the Coulombic efficiency of the battery and a shortening of the cycle life, seriously affecting the safety and stability of lithium metal batteries. Therefore, how to effectively inhibit the formation of lithium dendrites and improve the safety and stability of lithium batteries has become the focus of current research.

[0003] Currently, the strategies for inhibiting lithium dendrites mainly include: (1) designing novel electrolytes (such as high-concentration electrolytes, locally high-concentration electrolytes, ionic liquids, etc.), but they have high costs, limited conductivity, and strict requirements for environmental equipment; (2) constructing an artificial solid electrolyte interface layer (SEI), but the interface stability is poor, it is easy to break and fail, and it is difficult to industrialize; (3) using functionalized separators: improving lithium deposition behavior and extending the battery life. Among them, functionalized separators are considered one of the most effective solutions because they can directly block dendrite penetration, regulate the flow of lithium ions, and guide uniform deposition. However, the existing functionalized separators still have the following problems: (1) limited mechanical strength and cannot completely prevent dendrite penetration; (2) poor interface stability and may fall off or fail after long-term cycling; (3) can only act on physical barrier or chemical regulation alone and lack a synergistic mechanism.

[0004] Based on the above problems, the present invention proposes a novel polyimide-based composite separator with a dual mechanism for inhibiting lithium dendrite growth, which can effectively inhibit lithium dendrites through the dual mechanisms of mechanical barrier and chemical induction, and improve the cycle stability and safety of lithium batteries. Summary of the Invention

[0005] The object of the present invention is to provide a novel polyimide composition, a composite separator, a preparation method and a lithium battery using the separator and coating, which can inhibit the growth of lithium dendrites by a dual mechanism. The composite separator has the characteristics of high temperature resistance, high porosity, good chemical stability and high temperature dimensional stability, and improves the electrolyte wettability and flame retardancy of the separator. At the same time, when the composite separator is applied to a lithium battery, by constructing Li-Ag alloy and Li-Mg alloy respectively, the growth of lithium dendrites can be significantly inhibited, and the cycle stability and service life of the lithium battery can be improved.

[0006] 1. The present invention provides a novel polyimide-based composite separator for inhibiting the growth of lithium dendrites by a dual mechanism and a preparation method thereof. The separator is coated with a polyimide microsphere composition for inhibiting the growth of lithium dendrites by a dual mechanism, wherein the polyimide microsphere for inhibiting the growth of lithium dendrites by a dual mechanism is a polyimide microsphere with a poly(dopamine) protective layer and silver ions and magnesium ions loaded on the surface. After preparing the composition, it is coated on at least one side of a porous membrane. When used as a lithium battery separator, it can significantly inhibit the growth of lithium dendrites and improve the cycle stability and service life of the lithium battery.

[0007] A novel polyimide-based composite separator for inhibiting the growth of lithium dendrites by a dual mechanism and a preparation method thereof, characterized by comprising the following steps:

[0008] A: Synthesize a polyamic acid solution by solution polycondensation method. Dissolve polyamine in an organic solvent, add polyanhydride in batches, and mechanically stir in an ice-water bath to obtain a precursor solution (polyamic acid solution). Prepare polyamic acid microspheres by one of the methods of electrospray method, phase separation method, emulsion evaporation method, spray drying method, etc.; then perform high-temperature heat treatment to cyclize the polyamic acid to obtain polyimide microspheres.

[0009] B: Place the polyimide microspheres obtained in step A in an alkaline solution with a certain concentration, stir or ultrasonically treat them, and keep for a certain time. After the imide ring on the surface layer of the polyimide microspheres undergoes an alkali hydrolysis reaction to open the ring, wash with deionized water and dry; then immerse the microspheres in an acidic solution with a certain concentration, stir or ultrasonically treat them, wash with deionized water and dry to obtain polyimide microspheres with carboxyl groups on the surface.

[0010] C: Place the microspheres obtained in step B in a soluble silver salt solution with a certain concentration. After an ion exchange reaction, silver ions are complexed on the surface of the microspheres, wash with deionized water and dry to obtain polyimide microspheres with silver ions loaded on the surface.

[0011] D: Immerse the microspheres obtained in step C in a magnesium salt solution with a certain concentration, perform an ion exchange reaction again, wash with deionized water and dry to obtain polyimide microspheres with silver ions and magnesium ions loaded on the surface.

[0012] E: Place the microspheres obtained in step D into a dopamine solution, stir or perform ultrasonic treatment, and then perform drying treatment under a vacuum or nitrogen environment to obtain polyimide microspheres with a polydopamine protective layer and surface-loaded silver ions and magnesium ions.

[0013] F: Mix the polyimide microspheres with a polydopamine protective layer and surface-loaded silver ions and magnesium ions obtained in step E, a binder, a surfactant, a dispersant, and a solvent in a certain proportion, stir to prepare a composition, and then coat the composition on at least one side of a porous membrane by a certain method to obtain the novel polyimide-based composite separator for dual-mechanism inhibition of lithium dendrite growth.

[0014] Further, in the novel polyimide-based composite separator for dual-mechanism inhibition of lithium dendrite growth and its preparation method, the polyimide described in step A is any polyimide prepared by solution condensation polymerization of a polyanhydride and a polyamine. The solid content of the polyamic acid is 5 - 50%, preferably 10 - 20%. The organic solvent is any one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone. The temperature of the high-temperature heat treatment is 250 - 350°C, and the treatment time is 0.5 - 3 h.

[0015] Further, the alkaline solution described in step B is any one of lithium hydroxide, sodium hydroxide, and potassium hydroxide. The concentration of the alkaline solution is 0.01 - 6 mol / L. The time for stirring or ultrasonic treatment is 10 - 30 min. The time for washing with deionized water is 1 - 5 min. The drying temperature is 40 - 70°C, and the drying time is 10 - 90 min. The acidic solution is any one of formic acid, acetic acid, hydrochloric acid, and sulfuric acid. The concentration is 1 - 50 wt%. The time for stirring or ultrasonic treatment is 10 - 45 min. The time for washing with deionized water is 1 - 5 min. The drying temperature is 40 - 70°C, and the drying time is 10 - 90 min.

[0016] Further, the soluble silver salt solution described in step C is one or more of an aqueous solution of silver nitrate, silver fluoride, silver acetate, silver fluoroborate, silver benzoate, silver perchlorate, silver trifluoromethanesulfonate, and silver ammonia solution. The concentration is 0.1 - 2 mol / L. The time for the ion exchange reaction is 5 - 50 min. The time for washing with deionized water is 5 - 25 min. The drying temperature is 40 - 75°C, and the drying time is 10 - 120 min.

[0017] Further, the magnesium salt solution described in step D is an aqueous solution of one or more of magnesium chloride, magnesium nitrate, magnesium acetate, and magnesium formate, with a concentration of 0.1 - 2 mol / L. The time for the ion exchange reaction is 5 - 50 min, the time for washing with deionized water is 5 - 25 min, the drying temperature is 40 - 75 °C, and the drying time is 10 - 120 min.

[0018] Further, the concentration of the dopamine solution in step E is 0.5 - 2.0 mg / mL, the time for stirring or ultrasonic treatment is 6 - 12 h, the drying time under a vacuum or nitrogen environment is 5 - 30 h, and the drying temperature is 50 - 80 °C.

[0019] Further, the binder described in step F is one or a combination of two or more of polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethyl cellulose, polyurethane, styrene - butadiene rubber, fluorinated rubber, styrene - butadiene polymer, polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene, polyacrylic acid, polymethacrylic acid, polyacrylate, polymethyl methacrylate, and polyacrylonitrile; the surfactant is one or a combination of two or more of fluorocarbon surfactants (such as perfluoroalkyl ether alcohol amine salts, perfluoroalkyl ether quaternary ammonium salts), non - ionic surfactants (such as polyethylene glycol type, polyol type, block copolymer ether), cationic surfactants (such as cetyltrimethylammonium bromide, dodecyltrimethylammonium bromide, dodecylpyridinium bromide), and anionic surfactants (such as fatty acid salts, sulfonates, phosphates, and sulfates); the dispersant is one or a combination of two or more of cellulose ether - type dispersants such as hydroxypropyl methyl cellulose, hydroxyethyl cellulose, cellulose alkyl ether, or cellulose hydroxyalkyl ether, polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, polyacrylamide, and sodium polyacrylate; the solvent is one or a combination of two or more of deionized water, N - methylpyrrolidone, dimethyl sulfoxide, N,N - dimethylformamide, N,N - dimethylacetamide, and acetone; the ratio of the composition is 5 - 60 parts of polyimide microspheres with silver ions and magnesium ions loaded on the surface with a polydopamine protective layer, 0.1 - 15 parts of binder, 0.01 - 5 parts of surfactant, 0.01 - 10 parts of dispersant, and 30 - 100 parts of organic solvent; the time for mixing and stirring is 2 - 5 h; the coating method is one of concave coating, extrusion coating, transfer coating, dip coating, and wire bar coating, and the single - side coating thickness is 1 - 50 μm.

[0020] An article containing the composite separator prepared by the above - mentioned composite separator preparation method.

[0021] A lithium battery, which consists of a positive electrode, a negative electrode, an electrolyte, and a separator. It is characterized in that at least one of the components of the positive electrode, negative electrode, or separator of the battery contains the above - mentioned polyimide composition and coating for inhibiting lithium dendrite growth by a novel dual - mechanism.

[0022] Compared with the prior art, the present invention has the following excellent effects:

[0023] (1) After the lye etching and acidification treatment methods, the present invention innovatively loads silver ions and magnesium ions on the surface of polyimide microspheres successively, and then further uses polydopamine coating to enhance the ion adsorption stability. Finally, polyimide microspheres with silver ions and magnesium ions loaded on the surface with a polydopamine protective layer are formed. After being formulated into a composition and coated on at least one side of the porous membrane, a novel polyimide-based composite separator for dual-mechanism inhibition of lithium dendrite growth is prepared.

[0024] (2) A novel polyimide-based composite separator for dual-mechanism inhibition of lithium dendrite growth provided by the present invention has a stronger lithium dendrite inhibition ability when used as a lithium battery separator. Silver ions will promote the formation of Li-Ag alloy during the lithium metal deposition process, reduce the local current density, make the lithium deposition more uniform, and thus reduce the tip enhancement effect of dendrites; magnesium ions can alloy with lithium to form Li-Mg alloy, improve the mechanical strength of the negative electrode, and make it more difficult for dendrite penetration to occur; the polydopamine layer can stabilize silver and magnesium ions, improve the loading stability and prevent metal ions from precipitating and losing in the electrolyte. Since polydopamine itself has excellent adhesion and corrosion resistance, it can improve the chemical stability of the separator and at the same time improve the uniformity of the lithium ion channels, further optimizing the lithium deposition process.

[0025] (3) A novel polyimide-based composite separator for dual-mechanism inhibition of lithium dendrite growth provided by the present invention can improve the cycle life and Coulomb efficiency of lithium batteries. Through the synergistic effect of bimetallic ions, it can inhibit dendrite growth and maintain a stable electrochemical interface, greatly extending the battery cycle life; polydopamine, as a highly lithium-philic surface coating, can optimize the electrolyte wettability, improve the uniform distribution of lithium ions, reduce the "dead volume" loss of lithium, and improve the Coulomb efficiency.

[0026] (4) A novel polyimide-based composite separator for dual-mechanism inhibition of lithium dendrite growth provided by the present invention has higher thermal stability and safety compared with traditional polyolefin separators, can improve the interface stability, reduce the SEI film impedance, and is applicable to high-energy density lithium batteries, especially lithium metal batteries. Brief Description of the Drawings

[0027] Figure 1 SEM micrograph of the novel polyimide composite microspheres for dual-mechanism inhibition of lithium dendrite growth in Example 1;

[0028] Figure 2 SEM micrograph of the cross-section of the separator coated with the composition of the novel polyimide composite microspheres for dual-mechanism inhibition of lithium dendrite growth in Example 1;

[0029] Figure 3SEM cross-sectional microscopic morphology image of the separator coated with the polyimide composite microsphere composition for inhibiting lithium dendrite growth by a novel dual mechanism in Example 1;

[0030] Figure 4 C element map of the polyimide composite microsphere for inhibiting lithium dendrite growth by a novel dual mechanism in Example 1 in SEM test;

[0031] Figure 5 Ag element map of the polyimide composite microsphere for inhibiting lithium dendrite growth by a novel dual mechanism in Example 1 in SEM test;

[0032] Figure 6 SEM microscopic morphology image of the polyimide composite microsphere for inhibiting lithium dendrite growth by a novel dual mechanism in Example 5;

[0033] Figure 7 SEM microscopic morphology image of the polyimide microsphere in Comparative Example 1;

[0034] Figure 8 SEM cross-sectional microscopic morphology image of the separator coated with the polyimide microsphere composition in Comparative Example 1;

[0035] Figure 9 SEM microscopic morphology image of the polyimide-modified microsphere in Comparative Example 6; Detailed implementation manners

[0036] The following further elaborates the invention content in combination with the embodiments. It should be noted that the following embodiments are only used to illustrate the present invention and do not limit the technical solutions described in the present invention. Therefore, although this specification describes the present invention in detail with reference to the following embodiments, those skilled in the art should understand that any modifications or equivalent replacements that can be made to the present invention, and all technical solutions and their improvements that do not depart from the spirit core and scope of the present invention should be covered within the scope of the claims of the present invention.

[0037] Example 1

[0038] A polyimide-based composite separator for inhibiting lithium dendrite growth by a novel dual mechanism, and its preparation method includes the following steps:

[0039] (1) Preparation of novel polyimide composite microspheres with dual - mechanism inhibition of lithium dendrite growth: Prepare polyamic acid of the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N - dimethylformamide (DMF), and then add PMDA in batches. React under the condition of an ice - water bath at 0°C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10 - ml syringe and obtain polyamic acid microspheres through electrospray. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25°C, and receiving distance 20 cm. Place the microspheres in a high - temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260°C at a heating rate of 3°C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for 10 min, wash with deionized water for 5 min after treatment, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 0.2 mol / L silver nitrate solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 0.2 mol / L magnesium chloride solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 1 mol / L dopamine solution for 6 h, and then place in a nitrogen oven at 60°C for drying for 12 h to obtain polyimide microspheres with a poly - dopamine protective layer and surface - loaded silver ions and magnesium ions.

[0040] (2) Preparation of a novel polyimide-based composite separator for dual-mechanism inhibition of lithium dendrite growth: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then, weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir using a high-speed homogenizer with a rotation speed set at 8000 r / min and a stirring time of 60 min. The separator coating uses a microgravure coating process. Place the obtained polyimide composite microsphere composition in a vacuum oven for defoaming treatment for 1 h, and then evenly coat one or both sides of a 7-μm polyolefin separator using the microgravure coating method. Place the separator in a constant-temperature oven for drying at a drying temperature of 60 °C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7+4P, and the double-sided coated separator is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0041] Example 2

[0042] Differing from Example 1, in this example, potassium hydroxide solution is used in the alkali etching step, and other processes are the same as those in Example 1. The specific implementation steps are as follows:

[0043] (1) Preparation of novel polyimide composite microspheres with dual - mechanism inhibition of lithium dendrite growth: Prepare polyamic acid of the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N-dimethylformamide (DMF), and then add PMDA in batches. React under the condition of an ice - water bath at 0 °C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10 - ml syringe and obtain polyamic acid microspheres through electrospray. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25 °C, and receiving distance 20 cm. Place the microspheres in a high - temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260 °C at a heating rate of 3 °C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a potassium hydroxide solution for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for 10 min, wash with deionized water for 5 min after treatment, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 0.2 mol / L silver nitrate solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 0.2 mol / L magnesium chloride solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 1 mol / L dopamine solution for 6 h, and then place in a nitrogen oven at 60 °C for drying for 12 h to obtain polyimide microspheres with a poly - dopamine protective layer and surface - loaded silver ions and magnesium ions.

[0044] (2) Preparation of a novel polyimide-based composite separator with a dual mechanism for inhibiting lithium dendrite growth: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then, weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of an acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir using a high-speed homogenizer with a rotation speed set at 8000 r / min and a stirring time of 60 min. The separator coating uses a microgravure coating process. Place the obtained polyimide composite microsphere composition in a vacuum oven for defoaming treatment for 1 h, and then evenly coat one or both sides of a 7-μm polyolefin separator using the microgravure coating method. Place the separator in a constant-temperature oven for drying at a drying temperature of 60 °C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7 + 4P, and the double-sided coated separator is marked as 2P + 7 + 2P, where the numbers "4" and "2" represent the coating thickness.

[0045] Example 3

[0046] Differing from Example 1, in this example, formic acid is used as the acidic solution, and other processes are the same as those in Example 1. The specific implementation steps are as follows:

[0047] (1) Preparation of novel polyimide composite microspheres with dual - mechanism inhibition of lithium dendrite growth: Prepare polyamic acid of the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N - dimethylformamide (DMF), and then add PMDA in batches. React under the condition of an ice - water bath at 0°C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10 - ml syringe and obtain polyamic acid microspheres through electrospray. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25°C, and receiving distance 20 cm. Place the microspheres in a high - temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260°C at a heating rate of 3°C / min, hold for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in 5 wt% formic acid for 10 min, wash with deionized water for 5 min after treatment, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 0.2 mol / L silver nitrate solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 0.2 mol / L magnesium chloride solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 1 mol / L dopamine solution for 6 h, and then place in a nitrogen oven at 60°C for drying for 12 h to obtain polyimide microspheres with a poly - dopamine protective layer and surface - loaded silver ions and magnesium ions.

[0048] (2) Preparation of a novel polyimide-based composite separator with a dual-mechanism for inhibiting lithium dendrite growth: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then, weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of an acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir using a high-speed homogenizer with a rotation speed set at 8000 r / min for 60 min. The separator coating uses a microgravure coating process. Put the obtained polyimide composite microsphere composition into a vacuum oven for defoaming treatment for 1 h, and then uniformly coat one or both sides of a 7-μm polyolefin separator using the microgravure coating method. Place the separator in a constant-temperature oven for drying at a drying temperature of 60 °C for 15 min. The finally obtained single-sided coated separator is marked as 7 + 4P, and the double-sided coated separator is marked as 2P + 7 + 2P, where the numbers "4" and "2" represent the coating thickness.

[0049] Example 4

[0050] Differing from Example 1, in this example, the type of metal silver salt solution was adjusted, and other processes were the same as those in Example 1. The specific implementation steps are as follows:

[0051] (1) Preparation of novel polyimide composite microspheres with dual - mechanism inhibition of lithium dendrite growth: Prepare polyamic acid of the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N-dimethylformamide (DMF), and then add PMDA in batches. React under the condition of an ice - water bath at 0°C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10 - ml syringe and obtain polyamic acid microspheres through electrospray. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25°C, and receiving distance 20 cm. Place the microspheres in a high - temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260°C at a heating rate of 3°C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for 10 min, wash with deionized water for 5 min after treatment, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a silver ammonia solution with a silver ion concentration of 0.2 mol / L for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 0.2 mol / L magnesium chloride solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 1 mol / L dopamine solution for 6 h, and then place in a nitrogen oven at 60°C for drying for 12 h to obtain polyimide microspheres with a poly - dopamine protective layer and surface - loaded silver ions and magnesium ions.

[0052] (2) Preparation of a novel polyimide-based composite separator with dual-mechanism inhibition of lithium dendrite growth: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then, weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir using a high-speed homogenizer with a rotation speed set at 8000 r / min and a stirring time of 60 min. The separator coating adopts a microgravure coating process. Put the obtained polyimide composite microsphere composition into a vacuum oven for defoaming treatment for 1 h, and then uniformly coat it on one or both sides of a 7-μm polyolefin separator using the microgravure coating method. Place the separator in a constant-temperature oven for drying at a drying temperature of 60°C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7+4P, and the double-sided coated separator is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0053] Example 5

[0054] Different from Example 1, in this example, the concentration of the metal silver salt solution was adjusted, and other processes were the same as those in Example 1. The specific implementation steps are as follows:

[0055] (1) Preparation of novel polyimide composite microspheres with dual - mechanism inhibition of lithium dendrite growth: Prepare polyamic acid of the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N - dimethylformamide (DMF), and then add PMDA in batches. React under the condition of an ice - water bath at 0°C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10 - ml syringe and obtain polyamic acid microspheres through electrospray. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25°C, and receiving distance 20 cm. Place the microspheres in a high - temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260°C at a heating rate of 3°C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for 10 min, wash with deionized water for 5 min after treatment, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 0.5 mol / L silver nitrate solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 0.2 mol / L magnesium chloride solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 1 mol / L dopamine solution for 6 h, and then place in a nitrogen oven at 60°C for drying for 12 h to obtain polyimide microspheres with a poly - dopamine protective layer and surface - loaded silver ions and magnesium ions.

[0056] (2) Preparation of a novel polyimide-based composite separator for dual-mechanism inhibition of lithium dendrite growth: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then, weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir using a high-speed homogenizer with a rotation speed set at 8000 r / min and a stirring time of 60 min. The separator coating uses a microgravure coating process. Put the obtained polyimide composite microsphere composition into a vacuum oven for defoaming treatment for 1 h, and then evenly coat one or both sides of a 7-μm polyolefin separator by microgravure coating. Place the separator in a constant-temperature oven for drying at a drying temperature of 60 °C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7+4P, and the double-sided coated separator is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0057] Example 6

[0058] Different from Example 1, in this example, the concentration of the metal magnesium salt solution was adjusted, and other processes were the same as those in Example 1. The specific implementation steps are as follows:

[0059] (1) Preparation of novel polyimide composite microspheres with dual - mechanism inhibition of lithium dendrite growth: Prepare polyamic acid of the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N-dimethylformamide (DMF), and then add PMDA in batches. React under the condition of an ice - water bath at 0 °C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10 - ml syringe and obtain polyamic acid microspheres through electrospray. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25 °C, and receiving distance 20 cm. Place the microspheres in a high - temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260 °C at a heating rate of 3 °C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for 10 min, wash with deionized water for 5 min after treatment, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 0.2 mol / L silver nitrate solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 0.4 mol / L magnesium chloride solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 1 mol / L dopamine solution for 6 h, and then place in a nitrogen oven at 60 °C for drying for 12 h to obtain polyimide microspheres with a poly - dopamine protective layer and surface - loaded silver ions and magnesium ions.

[0060] (2) Preparation of a novel polyimide-based composite separator with a dual-mechanism for inhibiting lithium dendrite growth: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then, weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of an acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir using a high-speed homogenizer with a rotation speed set at 8000 r / min and a stirring time of 60 min. The separator coating uses a microgravure coating process. Place the obtained polyimide composite microsphere composition in a vacuum oven for defoaming treatment for 1 h, and then uniformly coat one or both sides of a 7-μm polyolefin separator using the microgravure coating method. Place the separator in a constant-temperature oven for drying at a drying temperature of 60°C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7 + 4P, and the double-sided coated separator is marked as 2P + 7 + 2P, where the numbers "4" and "2" represent the coating thickness.

[0061] Example 7

[0062] Differing from Example 1, in this example, the type of metal magnesium salt solution was adjusted, and other processes were the same as those in Example 1. The specific implementation steps are as follows:

[0063] (1) Preparation of novel polyimide composite microspheres with dual - mechanism inhibition of lithium dendrite growth: Prepare polyamic acid of the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N - dimethylformamide (DMF), and then add PMDA in batches. React under an ice - water bath condition at 0°C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10 - ml syringe and obtain polyamic acid microspheres through electrospray. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25°C, and receiving distance 20 cm. Place the microspheres in a high - temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260°C at a heating rate of 3°C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for 10 min, wash with deionized water for 5 min after treatment, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 0.2 mol / L silver nitrate solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 0.2 mol / L magnesium nitrate solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 1 mol / L dopamine solution for 6 h, and then place in a nitrogen oven at 60°C for drying for 12 h to obtain polyimide microspheres with a poly - dopamine protective layer and surface - loaded silver ions and magnesium ions.

[0064] Example 8

[0065] Differing from Example 1, in this example, the type of surfactant in the composition is changed, and other processes are the same as those in Example 1. The specific implementation steps are as follows:

[0066] (1) Preparation of novel polyimide composite microspheres with dual-mechanism inhibition of lithium dendrite growth: Prepare polyamic acid of the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N-dimethylformamide (DMF), and then add PMDA in batches. React under the condition of an ice-water bath at 0 °C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10 ml syringe and obtain polyamic acid microspheres through electrospray. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25 °C, and receiving distance 20 cm. Place the microspheres in a high-temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260 °C at a heating rate of 3 °C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for treatment for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for treatment for 10 min. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 0.2 mol / L silver nitrate solution for treatment for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 0.2 mol / L magnesium chloride solution for treatment for 6 h, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 5 h. Place the microspheres in a 1 mol / L dopamine solution for treatment for 6 h, and then place in a nitrogen oven at 60 °C for drying for 12 h to obtain polyimide microspheres with a poly-dopamine protective layer and surface-loaded silver ions and magnesium ions.

[0067] (2) Preparation of a novel polyimide-based composite separator with dual-mechanism inhibition of lithium dendrite growth: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then, weigh 2 g of dodecyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir using a high-speed homogenizer with a rotation speed set at 8000 r / min and a stirring time of 60 min. The separator coating uses a microgravure coating process. Put the obtained polyimide composite microsphere composition into a vacuum oven for defoaming treatment for 1 h, and then evenly coat one or both sides of a 7-μm polyolefin separator using the microgravure coating method. Place the separator in a constant-temperature oven for drying at a drying temperature of 60 °C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7 + 4P, and the double-sided coated separator is marked as 2P + 7 + 2P, where the numbers "4" and "2" represent the coating thickness.

[0068] Example 9

[0069] Differing from Example 1, in this example, the chemical structure of the polyimide was changed, and hexafluorodiacid anhydride (6FDA) with a trifluoromethyl group and 4,4'-biphenyl ether dianhydride (ODPA) monomer containing an ether oxygen bond were used. The other steps were the same as those in Example 1, and the specific implementation steps were as follows:

[0070] (1) Preparation of novel polyimide composite microspheres with dual-mechanism inhibition of lithium dendrite growth: Weigh the monomers hexafluorodiacetic anhydride (6FDA), 4,4'-oxydiphthalic anhydride (ODPA) and the monomer 4,4'-oxydianiline (ODA) according to 1.01:1. First, dissolve all of ODA in the solvent N,N-dimethylformamide (DMF), and then add 6FDA in batches. React under the condition of an ice-water bath at 0 °C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10 ml syringe and obtain polyamic acid microspheres by electrospray. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25 °C, and receiving distance 20 cm. Place the microspheres in a high-temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260 °C at a heating rate of 3 °C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for 10 min, wash with deionized water for 5 min after treatment, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 0.2 mol / L silver nitrate solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 0.2 mol / L magnesium chloride solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 1 mol / L dopamine solution for 6 h, and then place in a nitrogen oven at 60 °C for drying for 12 h to obtain polyimide microspheres with a poly-dopamine protective layer and surface-loaded silver ions and magnesium ions.

[0071] (2) Preparation of a novel polyimide-based composite separator with dual-mechanism inhibition of lithium dendrite growth: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then, weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir using a high-speed homogenizer with a rotation speed set at 8000 r / min and a stirring time of 60 min. The separator coating adopts a microgravure coating process. Put the obtained polyimide composite microsphere composition into a vacuum oven for defoaming treatment for 1 h, and then uniformly coat one or both sides of a 7-μm polyolefin separator by microgravure coating. Place the separator in a constant-temperature oven for drying at a drying temperature of 60 °C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7 + 4P, and the double-sided coated separator is marked as 2P + 7 + 2P, where the numbers "4" and "2" represent the coating thickness.

[0072] Example 10

[0073] Different from Example 1, in this example, the chemical structure of polyimide is changed, and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 4,4'-biphenylether dianhydride (ODPA) monomers containing ether oxygen bonds are used. Other steps are the same as those in Example 1, and the specific implementation steps are as follows:

[0074] (1) Preparation of novel polyimide composite microspheres with dual-mechanism inhibition of lithium dendrite growth: Weigh the monomers 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-oxydiphthalic dianhydride (ODPA) and the monomer 4,4'-oxydianiline (ODA) according to 1.01:1. First, dissolve all of ODA in the solvent N,N-dimethylformamide (DMF), and then add BPDA in batches. React for 3 h under the condition of an ice-water bath at 0 °C. Finally, obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10 ml syringe and obtain polyamic acid microspheres by electrospray. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25 °C, and receiving distance 20 cm. Place the microspheres in a high-temperature furnace for imidization treatment. The heating program is set as: heat from room temperature to 260 °C at a heating rate of 3 °C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for 10 min, wash with deionized water for 5 min after treatment, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 0.2 mol / L silver nitrate solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 0.2 mol / L magnesium chloride solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 1 mol / L dopamine solution for 6 h, and then place in a nitrogen oven at 60 °C for drying for 12 h to obtain polyimide microspheres with a poly-dopamine protective layer and surface-loaded silver ions and magnesium ions.

[0075] (2) Preparation of a novel polyimide-based composite separator with a dual mechanism for inhibiting lithium dendrite growth: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then, weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir using a high-speed homogenizer with a rotation speed set at 8000 r / min and a stirring time of 60 min. The separator coating uses a microgravure coating process. Place the obtained polyimide composite microsphere composition in a vacuum oven for defoaming treatment for 1 h, and then uniformly coat one or both sides of a 7-μm polyolefin separator using the microgravure coating method. Place the separator in a constant-temperature oven for drying at a drying temperature of 60 °C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7 + 4P, and the double-sided coated separator is marked as 2P + 7 + 2P, where the numbers "4" and "2" represent the coating thickness.

[0076] Example 11

[0077] Differing from Example 1, the concentration of the dopamine solution was changed in this example, and the other steps were the same as those in Example 1. The specific implementation steps are as follows:

[0078] (1) Preparation of novel polyimide composite microspheres with a dual - mechanism for inhibiting lithium dendrite growth: Prepare polyamic acid of the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N - dimethylformamide (DMF), and then add PMDA in batches. React for 3 h under the condition of an ice - water bath at 0 °C to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10 - ml syringe and obtain polyamic acid microspheres through electrospray. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25 °C, and receiving distance 20 cm. Place the microspheres in a high - temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260 °C at a heating rate of 3 °C / min, hold for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for 10 min, wash with deionized water for 5 min after treatment, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 0.2 mol / L silver nitrate solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 0.2 mol / L magnesium chloride solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 1.5 mol / L dopamine solution for 6 h, and then place in a nitrogen oven at 60 °C for drying for 12 h to obtain polyimide microspheres with a poly - dopamine protective layer and surface - loaded silver ions and magnesium ions.

[0079] (2) Preparation of a novel polyimide-based composite separator with a dual mechanism for inhibiting lithium dendrite growth: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then, weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of an acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir using a high-speed homogenizer with a rotation speed set at 8000 r / min and a stirring time of 60 min. The separator coating uses a microgravure coating process. Place the obtained polyimide composite microsphere composition in a vacuum oven for defoaming treatment for 1 h, and then uniformly coat one or both sides of a 7-μm polyolefin separator using the microgravure coating method. Place the separator in a constant-temperature oven for drying at a drying temperature of 60 °C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7 + 4P, and the double-sided coated separator is marked as 2P + 7 + 2P, where the numbers "4" and "2" represent the coating thickness.

[0080] Example 11

[0081] Different from Example 1, in this example, the treatment time of the metal silver salt solution and the magnesium salt solution is changed, and the other steps are the same as those in Example 1. The specific implementation steps are as follows:

[0082] (1) Preparation of novel polyimide composite microspheres with a dual - mechanism for inhibiting lithium dendrite growth: Prepare polyamic acid of the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N-dimethylformamide (DMF), and then add PMDA in batches. React under the condition of an ice - water bath at 0°C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10 - ml syringe and obtain polyamic acid microspheres through electrospray. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25°C, and receiving distance 20 cm. Place the microspheres in a high - temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260°C at a heating rate of 3°C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for 10 min, wash with deionized water for 5 min after treatment, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 0.2 mol / L silver nitrate solution for 20 min, then wash with deionized water for 3 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 0.2 mol / L magnesium chloride solution for 20 min, then wash with deionized water for 3 min, and then place in an oven at 60°C for drying for 15 min. Place the microspheres in a 1 mol / L dopamine solution for 6 h, and then place in a nitrogen oven at 60°C for drying for 12 h to obtain polyimide microspheres with a poly - dopamine protective layer and surface - loaded silver ions and magnesium ions.

[0083] (2) Preparation of a novel polyimide-based composite separator for inhibiting lithium dendrite growth by a dual mechanism: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then, weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of an acrylate adhesive with a solid content of 25%, and add them successively to the polyimide microsphere dispersion. Stir using a high-speed homogenizer with a rotation speed set at 8000 r / min and a stirring time of 60 min. The separator coating uses a microgravure coating process. Place the obtained polyimide composite microsphere composition in a vacuum oven for defoaming treatment for 1 h, and then evenly coat one or both sides of a 7-μm polyolefin separator using the microgravure coating method. Place the separator in a constant-temperature oven for drying at a drying temperature of 60 °C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7 + 4P, and the double-sided coated separator is marked as 2P + 7 + 2P, where the numbers "4" and "2" represent the coating thickness.

[0084] Comparative Example 1

[0085] A polyimide-based composite separator, and its preparation method includes the following steps:

[0086] (1) Preparation of polyimide microspheres: Prepare polyamic acid of the BPDA / ODA system. Weigh the monomers 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N-dimethylformamide (DMF), and then add BPDA in batches. React under an ice-water bath condition at 0 °C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and a moderate viscosity. Load this solution into a 10-ml syringe and obtain polyamic acid microspheres through electrospray. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25 °C, and receiving distance 20 cm. Place the microspheres in a high-temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260 °C at a heating rate of 3 °C / min, hold for 30 min, and then naturally cool to room temperature to obtain polyimide microspheres.

[0087] (2) Preparation of polyimide-based composite separator: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir using a high-speed homogenizer with the rotation speed set at 8000 r / min and the stirring time of 60 min. The separator coating adopts the microgravure coating process. Put the obtained polyimide microsphere composition into a vacuum oven for defoaming treatment for 1 h, and then evenly coat it on one or both sides of a 7-μm polyolefin separator by the microgravure coating method. Place the separator in a constant-temperature oven for drying at a drying temperature of 60 °C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7+4P, and the double-sided coated separator is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0088] Comparative Example 2

[0089] A polyimide-based composite separator, and its preparation method includes the following steps:

[0090] (1) Preparation of polyimide microspheres: Prepare polyamic acid of PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to the molar ratio of 1.01:1. First, dissolve all ODA in the solvent N,N-dimethylformamide (DMF), and then add PMDA in batches. React under the condition of an ice-water bath at 0 °C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10-ml syringe and obtain polyamic acid microspheres through electrostatic spraying. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25 °C, and receiving distance 20 cm. Place the microspheres in a high-temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260 °C at a heating rate of 3 °C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres.

[0091] (2) Preparation of polyimide-based composite separator: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir with a high-speed homogenizer, set the rotation speed to 8000 r / min, and the stirring time to 60 min. The separator coating adopts the microgravure coating process. Put the obtained polyimide microsphere composition into a vacuum oven for defoaming treatment for 1 h, and then evenly coat it on one or both sides of a 7-μm polyolefin separator by the microgravure coating method. Place the separator in a constant-temperature oven for drying, with the drying temperature at 60 °C and the drying time at 15 min. The finally obtained single-sided coated separator is marked as 7+4P, and the double-sided coated separator is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0092] Comparative Example 3

[0093] A polyimide-based composite separator, and its preparation method includes the following steps:

[0094] (1) Preparation of polyimide-modified microspheres: Prepare polyamic acid in the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N-dimethylformamide (DMF), and then add PMDA in batches. React under an ice-water bath condition at 0 °C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10-ml syringe and obtain polyamic acid microspheres by electrostatic spraying. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25 °C, and receiving distance 20 cm. Place the microspheres in a high-temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260 °C at a heating rate of 3 °C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for treatment for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for treatment for 10 min, wash with deionized water for 5 min after treatment, and then place in an oven at 60 °C for drying for 15 min.

[0095] (2) Preparation of polyimide-based composite separator: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir with a high-speed homogenizer, set the rotation speed to 8000 r / min, and the stirring time to 60 min. The separator coating adopts the microgravure coating process. Put the obtained polyimide microsphere composition into a vacuum oven for defoaming treatment for 1 h, and then evenly coat one or both sides of a 7-μm polyolefin separator by microgravure coating. Place the separator in a constant-temperature oven for drying, the drying temperature is 60 °C, and the drying time is 15 min. The finally obtained single-sided coated separator is marked as 7+4P, and the double-sided coated separator is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0096] Comparative Example 4

[0097] A polyimide-based composite separator, and its preparation method includes the following steps:

[0098] (1) Preparation of polyimide-modified microspheres: Prepare polyamic acid of PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to the molar ratio of 1.01:1. First, dissolve all ODA in the solvent N,N-dimethylformamide (DMF), and then add PMDA in batches. React under the condition of 0 °C ice-water bath for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10-ml syringe and obtain polyamic acid microspheres by electrostatic spraying. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25 °C, and receiving distance 20 cm. Place the microspheres in a high-temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260 °C at a heating rate of 3 °C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for 10 min, after treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 0.2 mol / L silver nitrate solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min.

[0099] (2) Preparation of polyimide-based composite separator: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir with a high-speed homogenizer, set the rotation speed to 8000 r / min, and the stirring time to 60 min. The separator coating adopts the microgravure coating process. Put the obtained polyimide microsphere composition into a vacuum oven for defoaming treatment for 1 h, and then evenly coat one or both sides of a 7-μm polyolefin separator by the microgravure coating method. Place the separator in a constant-temperature oven for drying, with a drying temperature of 60 °C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7+4P, and the double-sided coated separator is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0100] Comparative Example 5

[0101] A polyimide-based composite separator, and its preparation method includes the following steps:

[0102] (1) Preparation of polyimide-modified microspheres: Prepare polyamic acid in the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N-dimethylformamide (DMF), and then add PMDA in batches. React under the condition of an ice-water bath at 0 °C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10-ml syringe and obtain polyamic acid microspheres by electrostatic spraying. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25 °C, and receiving distance 20 cm. Place the microspheres in a high-temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260 °C at a heating rate of 3 °C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for treatment for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for treatment for 10 min. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in a 0.4 mol / L silver nitrate solution for treatment for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min.

[0103] (2) Preparation of polyimide-based composite separator: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then, weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir with a high-speed homogenizer, set the rotation speed to 8000 r / min, and the stirring time to 60 min. The separator coating adopts the microgravure coating process. Put the obtained polyimide microsphere composition into a vacuum oven for defoaming treatment for 1 h, and then evenly coat one or both sides of a 7-μm polyolefin separator by the microgravure coating method. Place the separator in a constant-temperature oven for drying, with a drying temperature of 60 °C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7+4P, and the double-sided coated separator is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0104] Comparative Example 6

[0105] A polyimide-based composite separator, and its preparation method includes the following steps:

[0106] (1) Preparation of polyimide-modified microspheres: Prepare polyamic acid in the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N-dimethylformamide (DMF), and then add PMDA in batches. React under an ice-water bath condition at 0 °C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10-ml syringe and obtain polyamic acid microspheres by electrostatic spraying. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25 °C, and receiving distance 20 cm. Place the microspheres in a high-temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260 °C at a heating rate of 3 °C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for 10 min. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 0.2 mol / L magnesium chloride solution for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min.

[0107] (2) Preparation of polyimide-based composite separator: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir with a high-speed homogenizer, set the rotation speed to 8000 r / min, and the stirring time to 60 min. The separator coating adopts the microgravure coating process. Put the obtained polyimide microsphere composition into a vacuum oven for defoaming treatment for 1 h, and then evenly coat one or both sides of a 7-μm polyolefin separator by microgravure coating. Place the separator in a constant-temperature oven for drying, with a drying temperature of 60 °C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7+4P, and the double-sided coated separator is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0108] Comparative Example 7

[0109] A polyimide-based composite separator, and its preparation method includes the following steps:

[0110] (1) Preparation of polyimide-modified microspheres: Prepare polyamic acid of the PMDA / ODA system. Weigh the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to a molar ratio of 1.01:1. First, dissolve all of the ODA in the solvent N,N-dimethylformamide (DMF), and then add PMDA in batches. React under the condition of an ice-water bath at 0 °C for 3 h to finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12 wt% and moderate viscosity. Load this solution into a 10-ml syringe and obtain polyamic acid microspheres by electrostatic spraying. The parameters of the spraying device are: voltage 20 kv, humidity 30%, temperature 25 °C, and receiving distance 20 cm. Place the microspheres in a high-temperature furnace for imidization treatment. The heating program is set as follows: heat from room temperature to 260 °C at a heating rate of 3 °C / min, keep warm for 30 min, and then cool naturally to room temperature to obtain polyimide microspheres. Place the polyimide microspheres in a sodium hydroxide solution for treatment for 10 min, where the concentration of the sodium hydroxide solution is 0.2 mol / L. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 5 wt% acetic acid for treatment for 10 min. After treatment, wash with deionized water for 5 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 0.2 mol / L silver chloride solution for treatment for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min. Place the microspheres in 0.2 mol / L magnesium chloride solution for treatment for 10 min, then wash with deionized water for 3 min, and then place in an oven at 60 °C for drying for 15 min.

[0111] (2) Preparation of polyimide-based composite separator: Weigh 200 g of microspheres and pour them into 400 g of N,N-dimethylformamide solvent to obtain a polyimide microsphere dispersion. Then weigh 2 g of cetyltrimethylammonium bromide powder, 4 g of sodium carboxymethylcellulose, and 20 g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion successively. Stir using a high-speed homogenizer with a rotation speed set at 8000 r / min and a stirring time of 60 min. The separator coating adopts the microgravure coating process. Put the obtained polyimide microsphere composition into a vacuum oven for defoaming treatment for 1 h, and then uniformly coat one or both sides of a 7-μm polyolefin separator by the microgravure coating method. Place the separator in a constant-temperature oven for drying at a drying temperature of 60 °C and a drying time of 15 min. The finally obtained single-sided coated separator is marked as 7+4P, and the double-sided coated separator is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0112] The above are only the preferred embodiments of the present invention, and do not limit the implementation manners and protection scope of the present invention accordingly. For those skilled in the art, it should be realized that all the equivalent replacements and obvious changes made by using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A novel dual-mechanism polyimide-based composite diaphragm for inhibiting lithium dendrite growth and a preparation method thereof, characterized in that: The diaphragm is coated with a polyimide microsphere composition that has a novel dual mechanism for inhibiting the growth of lithium dendrites, wherein the novel dual mechanism polyimide microspheres that inhibit the growth of lithium dendrites are polyimide microspheres with a polydopamine protective layer and surface-loaded with silver ions and magnesium ions. After the composition is prepared, it is coated on at least one side of a porous membrane. When used as a lithium battery diaphragm, it can significantly inhibit the growth of lithium dendrites and improve the cycle stability and service life of the lithium battery.

2. A novel dual-mechanism polyimide-based composite diaphragm for inhibiting lithium dendrite growth and a preparation method thereof as claimed in claim 1, characterized in that: The following steps are involved: A: A polyamic acid solution is synthesized by a solution polycondensation method, wherein a polyamine is dissolved in an organic solvent, a polyacid anhydride is added in batches, and a precursor solution (polyamic acid solution) is obtained by mechanical stirring in an ice-water bath; polyamic acid microspheres are prepared by an electrostatic spray method, a phase separation method, an emulsion evaporation method, or a spray drying method; and then a high-temperature heat treatment is performed to cyclize the polyamic acid to obtain polyimide microspheres; B: placing the polyimide microspheres obtained in step A in an alkaline solution of a certain concentration, stirring or ultrasonically treating, and maintaining for a certain period of time, so that the imide rings on the surface of the polyimide microspheres undergo alkaline hydrolysis to open the rings, and then washing with deionized water and drying; then immersing the microspheres in an acidic solution of a certain concentration, stirring or ultrasonically treating, washing with deionized water and drying, to obtain polyimide microspheres containing carboxyl groups on the surface; C: placing the microspheres obtained in step B in a soluble silver salt solution of a certain concentration, and undergoing an ion exchange reaction to complex silver ions on the surface of the microspheres, washing with deionized water and drying to obtain polyimide microspheres with silver ions loaded on the surface; D: immersing the microspheres obtained in step C into a magnesium salt solution of a certain concentration, performing an ion exchange reaction again, washing with deionized water and then drying to obtain polyimide microspheres with silver ions and magnesium ions loaded on the surface; E: placing the microspheres obtained in step D in a dopamine solution, stirring or ultrasonically treating, and then drying in a vacuum or nitrogen environment to obtain polyimide microspheres with a polydopamine protective layer and surface-loaded silver ions and magnesium ions; F: The polyimide microspheres with a polydopamine protective layer obtained in step E and loaded with silver ions and magnesium ions on the surface, a binder, a surfactant, a dispersant and a solvent are compounded in a certain proportion, stirred to obtain a composition, and then the composition is coated on at least one side of a porous membrane in a certain manner to obtain the novel polyimide-based composite diaphragm for inhibiting the growth of lithium dendrites by a dual mechanism.

3. A novel dual-mechanism polyimide-based composite diaphragm for inhibiting lithium dendrite growth and a preparation method according to claim 2, characterized in that: The polyimide described in step A is any polyimide prepared by solution condensation polymerization of a polyacid anhydride and a polyamine, and the solid content of the polyamic acid is 10-40wt%; the organic solvent is any one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; the temperature of the high-temperature heat treatment is 250-350°C, and the treatment time is 0.5-3h.

4. A novel dual-mechanism polyimide-based composite diaphragm for inhibiting lithium dendrite growth and a preparation method according to claim 2, characterized in that: The alkaline solution described in step B is any one of lithium hydroxide, sodium hydroxide, and potassium hydroxide, the concentration of the alkaline solution is 0.01-6 mol / L, the stirring or ultrasonic treatment time is 10-30 min, the deionized water washing time is 1-5 min, the drying temperature is 40-70 ° C, and the drying time is 10-90 min; the acidic solution is any one of formic acid, acetic acid, hydrochloric acid, and sulfuric acid, the concentration is 1-50wt%, the stirring or ultrasonic treatment time is 10-45 min, the deionized water washing time is 1-5 min, the drying temperature is 40-70 ° C, and the drying time is 10-90 min.

5. A novel dual-mechanism polyimide-based composite diaphragm for inhibiting lithium dendrite growth and a preparation method according to claim 2, characterized in that: The soluble silver salt solution described in step C is one or more of silver nitrate, silver fluoride, silver acetate, silver fluoroborate, silver benzoate, silver perchlorate, silver trifluoromethanesulfonate aqueous solution, and silver ammonia solution, with a concentration of 0.1-2 mol / L, an ion exchange reaction time of 5-50 min, a deionized water washing time of 5-25 min, a drying temperature of 40-75 ° C, and a drying time of 10-120 min.

6. A novel dual-mechanism polyimide-based composite diaphragm for inhibiting lithium dendrite growth and a preparation method according to claim 2, characterized in that: The magnesium salt solution described in step D is an aqueous solution of one or more of magnesium chloride, magnesium nitrate, magnesium acetate, and magnesium formate, with a concentration of 0.1-2 mol / L, an ion exchange reaction time of 5-50 min, a deionized water washing time of 5-25 min, a drying temperature of 40-75 ° C, and a drying time of 10-120 min.

7. A novel dual-mechanism polyimide-based composite diaphragm for inhibiting lithium dendrite growth and a preparation method according to claim 2, characterized in that: In step E, the concentration of the dopamine solution is 0.5-2.0 mg / mL, the stirring or ultrasonic treatment time is 6-12 hours, the drying time under vacuum or nitrogen environment is 5-30 hours, and the drying temperature is 50-80°C.

8. A novel dual-mechanism polyimide microsphere composition and coating for inhibiting lithium dendrite growth, characterized in that: The polyimide microspheres with surface-loaded silver ions and magnesium ions having a polydopamine protective layer prepared by the method of claim 2, a binder, a surfactant, a dispersant and a solvent are compounded in a certain proportion; the binder in step F is one or a combination of two or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyacrylic acid, polymethacrylic acid, polyacrylate, polymethyl methacrylate and polyacrylonitrile; the surfactant is a fluorocarbon surfactant (such as perfluoroalkyl ether alcohol amine salt, perfluoroalkyl ether quaternary ammonium salt), a nonionic surfactant (such as polyethylene glycol type, polyol type, block copolyether), a cationic surfactant (such as hexadecyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, dodecyl pyridinium bromide), an anionic surfactant (such as fatty acid salt, sulfonate, phosphate and sulfate ester salt) The dispersant is one or a combination of two or more of cellulose ether dispersants such as hydroxypropyl methylcellulose, hydroxyethyl cellulose, cellulose alkyl ether or cellulose hydroxyalkyl ether, polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, polyacrylamide, and sodium polyacrylate; the solvent is one or a combination of two or more of deionized water, N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and acetone; the proportion of the composition is 5-60 parts of polyimide microspheres with a polydopamine protective layer and surface-loaded silver ions and magnesium ions, 0.1-15 parts of a binder, 0.01-5 parts of a surfactant, 0.01-10 parts of a dispersant, and 30-100 parts of a solvent; the mixing time is 2-5 hours; the composition is coated, and the coating method is one of concave coating, extrusion coating, transfer coating, dip coating, and wire rod coating, and the single-sided coating thickness is 1-50 μm.

9. A composite diaphragm made by the preparation method of the polyimide composite diaphragm according to any one of claims 1 to 8.

10. A lithium battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that: The novel polyimide composition and coating for inhibiting lithium dendrite growth by dual mechanism according to claims 1 to 9 are contained on at least one component of the positive electrode, negative electrode or separator of the battery.

Images