Polyimide composite microsphere composition with lithium dendrite inhibiting function, coated diaphragm and coated electrode

Abstract

The invention discloses a polyimide composite microsphere composition with a lithium dendrite inhibiting function, a coated diaphragm and a coated electrode. The polyimide composite microsphere composition with the lithium dendrite inhibiting function is prepared from polyimide composite microspheres, a binder, a surfactant, a dispersing agent and a solvent, the polyimide composite microspheres are polyimide microspheres of which the shallow surface layer is loaded with silver nanocrystals; the coated diaphragm and the electrode are obtained by coating the composition on the surface of at least one side of a base membrane or an electrode plate in a micro-concave coating, extrusion coating, transfer coating, dip coating or bar coating mode and then drying. When the composition is used as a coating material, the lithium ion deposition behavior can be optimized, the cycle life of a battery is prolonged, the growth of lithium dendrites is effectively inhibited, the safety of the battery is improved, and the composition has important significance on promoting the development of a high-performance lithium battery. In addition, the composition provided by the invention has high matching degree with an existing coating process, has extremely high production efficiency, and is beneficial to realizing large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a polyimide composite microsphere composition having a function of inhibiting lithium dendrites, a coated diaphragm and a coated electrode. Background Art

[0002] Lithium-ion batteries have developed rapidly due to their advantages such as high specific capacity, long cycle life, clean and pollution-free, and small size. However, with the widespread use of lithium-ion batteries, it has been found that after multiple charge and discharge cycles, due to the uneven transmission and deposition of lithium ions, it is very easy to reduce to tree-like metallic lithium on the lithium negative electrode side, which is called "lithium dendrites". The growth of lithium dendrites will continuously consume electrolyte, causing the battery capacity to decay rapidly and the coulomb efficiency to be low. If the growing lithium dendrites pierce the diaphragm, it will also cause internal short circuit and thermal runaway of the battery, causing the risk of combustion and explosion.

[0003] As a key component of lithium-ion batteries, the diaphragm has an important influence on the performance of the battery. At present, improving the usability and safety of the battery by inhibiting the growth of lithium dendrites through the diaphragm is one of the hot spots in lithium battery research. Scientists have developed a ceramic-coated wet-process polyolefin composite diaphragm to improve the temperature resistance and wettability of the diaphragm. The composite diaphragm is composed of ceramic particles, a binder, other additives and a wet-process polyolefin diaphragm. The modified ceramic-coated polyolefin diaphragm obtained in this way has good thermal dimensional stability and electrolyte wettability, and has the original mechanical and mechanical properties of the polyolefin diaphragm. However, there are still some problems with the ceramic particle-coated polyolefin diaphragm, such as the large bulk density of the ceramic particles, which will cause the surface density of the coated diaphragm to increase significantly, thereby causing the battery energy density to decrease. Therefore, using a low-density high-temperature resistant polymer as a coating material for the polyolefin diaphragm can effectively solve the problem of high surface density of the coated diaphragm. The unique imide ring structure on the polyimide main chain gives it many excellent properties: such as high and low temperature resistance, corrosion resistance, radiation resistance, excellent mechanical properties, low thermal expansion coefficient, low dielectric constant, etc. Polyimide microspheres are of micro-nano size and inherit all the excellent properties of polyimide, especially high temperature resistance, strong molecular surface modifiability, good chemical stability, and sustained release function. At the same time, they also have the characteristics of large specific surface area of ​​microspheres. As a coating material, polyimide microspheres have significant effects in improving the temperature resistance and wettability of the diaphragm, and play a vital role in improving battery safety. While maintaining the excellent performance of the polyimide microsphere-coated diaphragm, in order to further improve its comprehensive performance and give it the ability to inhibit lithium dendrites, thereby expanding its practical application value, it is also a very challenging and forward-looking direction in this field. However, there are currently no reports on how to incorporate the function of inhibiting lithium dendrites into the coating of polyimide microspheres.

[0004] To this end, the present invention invents a polyimide composite microsphere composition with the function of inhibiting lithium dendrites, the composition is composed of polyimide composite microspheres, a binder, a surfactant, a dispersant and a solvent, wherein the polyimide composite microspheres are polyimide microspheres with a shallow surface layer loaded with silver (Ag) nanocrystals, and the nucleation overpotential of lithium ions is reduced by introducing a lithium-philic metal, thereby promoting homogeneous nucleation, and combining the high temperature resistance and excellent mechanical properties of the polyimide microspheres to form a composite material with excellent anti-dendrite function. The composition is coated on the surface of the battery separator and the electrode, which can effectively inhibit the growth of lithium dendrites and improve the cycle stability and service life of the lithium-ion battery. Summary of the invention

[0005] The purpose of the present invention is to provide a polyimide composite microsphere composition with the function of inhibiting lithium dendrites, a coated diaphragm and a coated electrode. The composition is formed by combining polyimide composite microspheres with other functional materials, wherein the polyimide composite microspheres are polyimide microspheres with silver nanocrystals loaded on the shallow surface layer. The composition is coated on the surface of the diaphragm and the electrode, which can significantly inhibit the growth of lithium dendrites and improve the cycle stability and service life of lithium-ion batteries.

[0006] 1. The present invention provides a polyimide composite microsphere composition and coating with the function of inhibiting lithium dendrites, characterized in that the composition consists of polyimide composite microspheres, a binder, a surfactant, a dispersant and a solvent, wherein the polyimide composite microspheres are 5-59 parts, the binder is 0.1-10 parts, the surfactant is 0.01-3 parts, the dispersant is 0.01-8 parts, and the solvent is 40-95 parts.

[0007] Furthermore, the binder 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.

[0008] Furthermore, 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 hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, dodecylpyridinium bromide; an anionic surfactant, such as one or a combination of two or more of fatty acid salts, sulfonates, phosphates and sulfates, preferably a fluorocarbon surfactant and a nonionic surfactant.

[0009] Furthermore, the dispersant is one or a combination of two or more of hydroxypropyl methylcellulose, hydroxyethyl cellulose, cellulose alkyl ether or cellulose hydroxyalkyl ether and other cellulose ether dispersants, polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, polyacrylamide, sodium polyacrylate, preferably hydroxypropyl methylcellulose and polyacrylamide.

[0010] Furthermore, the solvent is an organic solvent or an aqueous solvent, the organic solvent is one or a combination of two or more of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and acetone, and the aqueous solvent is pure water or one or a combination of two or more of water and ethanol, ethylene glycol, propanol, glycerol, isopropanol, and butanol.

[0011] Furthermore, the coating is formed by coating the above composition and then drying it.

[0012] 2. The present invention provides a polyimide composite microsphere composition and coating with the function of inhibiting lithium dendrites, characterized in that the polyimide composite microspheres with the function of inhibiting lithium dendrites are polyimide microspheres loaded with silver nanocrystals on the shallow surface, the particle size of the polyimide microspheres is 0.02μm-10μm, and the particle size range of the silver nanocrystals is 0.01μm-2μm.

[0013] A polyimide composite microsphere with the function of inhibiting lithium dendrites and a preparation method thereof, characterized in that the process comprises the following steps:

[0014] A: The polyamic acid solution is synthesized by a solution polycondensation method, wherein a diamine is dissolved in an organic solvent, and a dibasic acid anhydride is added in batches, and the precursor solution (polyamic acid solution) is obtained by mechanical stirring in an ice water bath. The polyamic acid microspheres are prepared by one of an electrostatic spray method, a phase separation method, an emulsion evaporation method, and a spray drying method.

[0015] B: subjecting the polyamic acid microspheres to high temperature heat treatment to cause thermal imidization of the polyamic acid to obtain polyimide microspheres.

[0016] C: placing the microspheres obtained in step B in an alkaline solution of a certain concentration, stirring or ultrasonically treating the solution, and maintaining the solution for a certain period of time, so that the imide rings on the surface of the polyimide microspheres undergo alkaline hydrolysis and ring opening.

[0017] D: The microspheres obtained in step C are washed with deionized water and dried, then immersed in an acid solution of a certain concentration for acidification, stirred or ultrasonically treated, and washed with deionized water to obtain polyimide microspheres containing carboxyl groups on the surface.

[0018] E: The microspheres obtained in step D are placed in a soluble silver salt solution of a certain concentration for treatment. After an ion exchange reaction, the silver ions are complexed to the surface of the microspheres. The microspheres are washed with deionized water and dried to finally obtain polyimide microspheres with surface-loaded silver ions.

[0019] F: The polyimide microspheres with surface loaded silver ions obtained in step E are subjected to reduction treatment to obtain polyimide microspheres with surface silver.

[0020] Furthermore, 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%, preferably 12-16wt%.

[0021] Furthermore, the organic solvent is any one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

[0022] Furthermore, the high temperature heat treatment described in step B has a treatment temperature of 260-300° C. and a treatment time of 0.5-1 h.

[0023] Furthermore, the alkaline solution in step C is any one of sodium hydroxide, potassium hydroxide and lithium hydroxide, with a concentration of 0.01-5 mol / L, preferably 0.1-0.3 mol / L, and the stirring or ultrasonic treatment time is 5-45 min.

[0024] Furthermore, the deionized water washing time in step D is 3-10 min, the drying temperature is 40-70° C., and the drying time is 10-100 min; the acidic solution is any one of formic acid, acetic acid, hydrochloric acid, and sulfuric acid, with a concentration of 1-30 wt%, and the stirring or ultrasonic treatment time is 5-45 min.

[0025] Furthermore, in step E, the metal silver salt solution is one or more of an aqueous solution of silver nitrate, silver fluoride, silver acetate, silver fluoroborate, silver benzoate, silver perchlorate, silver trifluoromethanesulfonate, and a silver ammonia solution, the concentration of the metal silver salt solution is 0.1-1.5 mol / L, and the treatment time is 5-45 min; the deionized water is used for washing for 3-10 min, the drying temperature is 40-70° C., and the drying time is 10-100 min.

[0026] Furthermore, the reduction treatment of silver ions in step F is chemical reduction or thermal reduction, the reducing agent used in the chemical reduction is one or more of dimethylamine borane (DMAB) solution, hydrazine hydrate solution, alkaline glucose solution and ascorbic acid solution, the concentration is 0.01-0.2 mol / L, and the reduction time is 5-60 min; the temperature used in the thermal reduction is 290-310° C., preferably 300° C., and the reduction time is 1-8 h.

[0027] 3. The present invention also provides a polyimide composite microsphere composition coated diaphragm with the function of inhibiting lithium dendrites, characterized in that the coated diaphragm is obtained by coating the polyimide composite microsphere composition of the present invention on at least one side of the porous membrane, and the single-sided coating thickness is 1-20 μm.

[0028] Furthermore, the porous base membrane is one of a polyolefin membrane, a cellulose membrane, a polyester membrane, a nanofiber nonwoven membrane, and an aramid membrane; preferably, the porous membrane is a polyolefin membrane.

[0029] The method of coating the diaphragm with polyimide composite microspheres that inhibit lithium dendrites is one of micro-dimple coating, extrusion coating, transfer coating, dip coating, and wire rod coating.

[0030] 4. The present invention also provides a polyimide composite microsphere composition coated electrode with the function of inhibiting lithium dendrites, characterized in that the coated electrode is obtained by coating the polyimide composite microsphere composition of the present invention on at least one side of the surface of the negative electrode sheet, and the single-sided coating thickness is 1-20 μm.

[0031] The method of coating the polyimide composite microsphere electrode with the function of inhibiting lithium dendrites is one of micro-dimple coating, extrusion coating, transfer coating, dip coating and wire rod coating.

[0032] A product comprises the polyimide composite microsphere composition having the function of inhibiting lithium dendrites, a coated diaphragm and a coated electrode.

[0033] A lithium ion battery, characterized in that the lithium ion battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator arranged between the positive electrode and the negative electrode.

[0034] A lithium ion battery, characterized in that the lithium ion battery consists of a positive electrode, a separator, an electrolyte and the negative electrode plate.

[0035] Compared with the prior art, the present invention has the following excellent effects:

[0036] (1) The polyimide composite microsphere composition and coating with the function of inhibiting lithium dendrites provided by the present invention have a high degree of compatibility with the existing coating process. Whether it is coating a diaphragm or an electrode, it has extremely high production efficiency and is conducive to large-scale production.

[0037] (2) The present invention provides a composition and coating of polyimide composite microspheres with the function of inhibiting lithium dendrites. When used as a coating material for a lithium battery separator, it has better adhesion to the base film while maintaining the coating density, thereby having better resistance to heat shrinkage and reducing the risk of thermal runaway. The separator coated with the coating can optimize the lithium ion deposition behavior, make the electric field distribution of lithium ion deposition more uniform, significantly extend the battery cycle life, effectively prevent dendrites from penetrating the separator, and improve battery safety.

[0038] (3) The present invention provides a composition and coating of polyimide composite microspheres with the function of inhibiting lithium dendrites. When used as a coating material to coat an electrode, the coating layer effectively inhibits the growth of lithium dendrites, reduces the frequency of side reactions on the electrode surface, and extends the battery life; at the same time, it reduces the risk of dendrites piercing the diaphragm, significantly improving the safety performance of the battery; in addition, it provides a more stable interface resistance and lower voltage fluctuations, thereby improving the rate performance and capacity retention rate of the battery.

[0039] (4) The present invention can prepare a polyimide composite microsphere with the function of inhibiting lithium dendrites through simple operations, that is, a polyimide microsphere loaded with silver nanocrystals on the shallow surface. The process flow is relatively simple, the adjustable range is large, the cost is low, and the application range is very wide.

[0040] (5) The polyimide composite microspheres prepared by the present invention have the function of inhibiting lithium dendrites, which are characterized by light weight and large specific surface area. In addition, the polyimide composite microspheres have the advantages of low cost and low density compared with pure metals, and have a smaller density than ceramic particles and better compatibility with polymer base films. When used as a coating material, the coating and the base film have better adhesion, are not easy to fall off, have higher peel strength, and have high material utilization. The surface density of the coated diaphragm can be significantly reduced, which is beneficial to improving the energy density of the battery. It has broad application prospects in the field of lightweight new energy devices.

[0041] (6) The polyimide composite microspheres with the function of inhibiting lithium dendrites prepared by the present invention can adjust the diameter of the polyimide microspheres and the diameter of the loaded silver nanocrystals to meet the needs of different fields, making it possible to mass-produce such polyimide composite microspheres instead of metallic silver as a coating material.

[0042] (7) The polyimide composite microspheres with the function of inhibiting lithium dendrites prepared by the present invention have a strong versatility in preparation method, are applicable to all polyimide systems, and can also be extended to the application modification of other types of polymer microspheres.

[0043] (8) The present invention provides a polyimide composite microsphere composition with the function of inhibiting lithium dendrites, which is coated on the diaphragm. The electrolyte distribution and lithium ion deposition behavior are regulated by the functionalized coating, thereby effectively inhibiting the growth of lithium dendrites and improving the safety and cycle life of the lithium battery.

[0044] (9) The polyimide composite microsphere composition coated electrode with the function of inhibiting lithium dendrites provided by the present invention can effectively inhibit the growth of lithium dendrites and improve the cycle stability and safety performance of the battery through structural design and function regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a SEM microscopic morphology picture of the polyimide composite microspheres that inhibit lithium dendrites in Example 1;

[0046] Figure 2 This is a cross-sectional SEM microscopic morphology picture of the polyimide composite microsphere composition coated with the separator having the function of inhibiting lithium dendrites in Example 1;

[0047] Figure 3 This is a cross-sectional SEM microscopic morphology picture of the polyimide composite microsphere coated separator having the function of inhibiting lithium dendrites in Example 1;

[0048] Figure 4 This is a SEM microscopic morphology picture of the polyimide composite microspheres with the function of inhibiting lithium dendrites in Example 7;

[0049] Figure 5 This is the SEM microscopic morphology picture of the polyimide microspheres in Comparative Example 1; DETAILED DESCRIPTION

[0050] The following examples are combined to further illustrate the content of the invention. It should be noted that the following examples are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although this specification describes the present invention in detail with reference to the following examples, it should be understood by those skilled in the art that any technical solutions and improvements that can be modified or equivalently replaced with the present invention and that do not deviate from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

[0051] Example 1

[0052] A polyimide composite microsphere composition coated diaphragm having a lithium dendrite inhibiting function, and a preparation method thereof comprises the following steps:

[0053] (1) Preparation of polyimide composite microspheres with lithium dendrite inhibition function: Prepare polyamic acid of PMDA / ODA system, weigh the monomer pyromellitic anhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to the molar ratio of 1.01:1, first dissolve all ODA in solvent N,N-dimethylformamide (DMF), then add PMDA in batches, and react for 3 hours under 0℃ ice water bath conditions, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were placed in a sodium hydroxide solution for 10 minutes, wherein the concentration of the sodium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in 3wt% acetic acid for 10 minutes, washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in a 0.2mol / L silver nitrate solution for 10 minutes, then washed with deionized water for 3 minutes, and then dried in a 60°C oven for 15 minutes. The polyimide microspheres loaded with silver ions on the surface were immersed in a 0.1mol / L DMAB solution for 15 minutes for reduction treatment to obtain polyimide composite microspheres loaded with silver nanocrystals on the shallow surface.

[0054] (2) Preparation of polyimide composite microsphere composition and coated diaphragm with lithium dendrite inhibition function: Weigh 200g microspheres, pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g hexadecyltrimethylammonium bromide powder, 4g sodium carboxymethyl cellulose, and 20g acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir with a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. The diaphragm coating adopts a micro-concave coating process, and the obtained polyimide composite microsphere composition is placed in a vacuum oven for defoaming treatment for 1h, and then evenly coated on one or both sides of a 7μm polyolefin diaphragm by micro-concave coating. The diaphragm was placed in a constant temperature oven to dry at 60°C for 15 minutes. The final single-sided coated diaphragm was marked as 7+4P, and the double-sided coated diaphragm was marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0055] Example 2

[0056] The difference from Example 1 is that the type of surfactant in the composition is changed in this example, and the other steps are the same as those in the example. The specific implementation steps are as follows:

[0057] (1) Preparation of polyimide composite microspheres with lithium dendrite inhibition function: Prepare polyamic acid of PMDA / ODA system, weigh the monomer pyromellitic anhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to the molar ratio of 1.01:1, first dissolve all ODA in solvent N,N-dimethylformamide (DMF), then add PMDA in batches, and react for 3 hours under 0℃ ice water bath conditions, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were placed in a sodium hydroxide solution for 10 minutes, wherein the concentration of the sodium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in 3wt% acetic acid for 10 minutes, washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in a 0.2mol / L silver nitrate solution for 10 minutes, then washed with deionized water for 3 minutes, and then dried in a 60°C oven for 15 minutes. The polyimide microspheres loaded with silver ions on the surface were immersed in a 0.1mol / L DMAB solution for 15 minutes for reduction treatment to obtain polyimide composite microspheres loaded with silver nanocrystals on the shallow surface.

[0058] (2) Preparation of polyimide composite microsphere composition and coated diaphragm with the function of inhibiting lithium dendrites: Weigh 200g of microspheres, pour into a mixed solvent of 395g of water and 5g of ethanol to obtain a polyimide microsphere dispersion, then weigh 2g of dodecyltrimethylammonium bromide powder, 4g of sodium carboxymethyl cellulose, and 20g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir with a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. The diaphragm coating adopts a micro-concave coating process, and the obtained polyimide composite microsphere composition is placed in a vacuum oven for defoaming treatment for 1h, and then evenly coated on one or both sides of a 7μm polyolefin diaphragm by micro-concave coating. The diaphragm was placed in a constant temperature oven to dry at 60°C for 15 minutes. The final single-sided coated diaphragm was marked as 7+4P, and the double-sided coated diaphragm was marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0059] Example 3

[0060] Different from Example 1, this example changes the chemical structure of polyimide, and uses hexafluorodianhydride (6FDA) with trifluoromethyl and 4,4'-biphenyl ether dianhydride (ODPA) monomers containing ether oxygen bonds. The other steps are the same as those in Example 1, and the specific implementation steps are as follows:

[0061] (1) Preparation of polyimide composite microspheres with lithium dendrite inhibition function: The monomer hexafluorodianhydride (6FDA), 4,4'-biphenyl ether dianhydride (ODPA) and the monomer 4,4'-diaminodiphenyl ether (ODA) were weighed in a ratio of 1.01:1, and the ODA was first completely dissolved in the solvent N,N-dimethylformamide (DMF), and then 6FDA was added in batches, and reacted in an ice-water bath at 0°C for 3 hours, and finally a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity was obtained. The solution was filled into a 10ml syringe and polyamic acid microspheres were obtained by electrostatic spraying, wherein the parameters of the spray device were: voltage 20kv, humidity 30%, temperature 25°C, and receiving distance 20cm. The microspheres were placed in a high-temperature hot furnace for imidization treatment, and the heating program was set as: heating from room temperature to 260°C at a heating rate of 3°C / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were placed in a sodium hydroxide solution for 10 minutes, wherein the concentration of the sodium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in 3wt% acetic acid for 10 minutes, washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in a 0.2mol / L silver nitrate solution for 10 minutes, washed with deionized water for 3 minutes, and then dried in a 60°C oven for 15 minutes. The polyimide microspheres loaded with silver ions on the surface were immersed in a 0.1mol / L DMAB solution for 15 minutes for reduction treatment to obtain polyimide composite microspheres loaded with silver nanocrystals on the shallow surface.

[0062] (2) Preparation of polyimide composite microsphere composition and coated diaphragm with lithium dendrite inhibition function: Weigh 200g microspheres, pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g hexadecyltrimethylammonium bromide powder, 4g sodium carboxymethyl cellulose, and 20g acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir with a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. The diaphragm coating adopts a micro-concave coating process, and the obtained polyimide composite microsphere composition is placed in a vacuum oven for defoaming treatment for 1h, and then evenly coated on one or both sides of a 7μm polyolefin diaphragm by micro-concave coating. The diaphragm was placed in a constant temperature oven to dry at 60°C for 15 minutes. The final single-sided coated diaphragm was marked as 7+4P, and the double-sided coated diaphragm was marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0063] Example 4

[0064] Different from Example 1, this example changes the chemical structure of polyimide and uses 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) and 4,4'-biphenyl ether dianhydride (ODPA) monomers containing ether oxygen bonds. The other steps are the same as those in Example 1, and the specific implementation steps are as follows:

[0065] (1) Preparation of polyimide composite microspheres with lithium dendrite inhibition function: The monomers 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), 4,4'-biphenyl ether dianhydride (ODPA) and 4,4'-diaminodiphenyl ether (ODA) were weighed in a ratio of 1.01:1, and the ODA was first completely dissolved in the solvent N,N-dimethylformamide (DMF), and then BPDA was added in batches, and reacted in an ice-water bath at 0°C for 3 hours, and finally a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity was obtained. The solution was filled into a 10ml syringe and polyamic acid microspheres were obtained by electrostatic spraying, wherein the parameters of the spray device were: voltage 20kv, humidity 30%, temperature 25°C, and receiving distance 20cm. The microspheres were placed in a high-temperature furnace for imidization treatment, and the heating program was set as follows: the temperature was raised from room temperature to 260°C at a heating rate of 3°C / min, and then naturally cooled to room temperature after 30 minutes of heat preservation to obtain polyimide microspheres. The polyimide microspheres were placed in a sodium hydroxide solution for 10 minutes, wherein the concentration of the sodium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes after treatment, and then placed in a 60°C oven for drying for 15 minutes. The microspheres were placed in 3wt% acetic acid for 10 minutes, washed with deionized water for 5 minutes after treatment, and then placed in a 60°C oven for drying for 15 minutes. The microspheres were placed in a 0.2mol / L silver nitrate solution for 10 minutes, washed with deionized water for 3 minutes, and then placed in a 60°C oven for drying for 15 minutes. The polyimide microspheres loaded with silver ions on the surface were immersed in a 0.1mol / L DMAB solution for 15 minutes for reduction treatment to obtain polyimide composite microspheres loaded with silver nanocrystals on the shallow surface.

[0066] (2) Preparation of polyimide composite microsphere composition and coated diaphragm with lithium dendrite inhibition function: Weigh 200g microspheres, pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g hexadecyltrimethylammonium bromide powder, 4g sodium carboxymethyl cellulose, and 20g acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir with a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. The diaphragm coating adopts a micro-concave coating process, and the obtained polyimide composite microsphere composition is placed in a vacuum oven for defoaming treatment for 1h, and then evenly coated on one or both sides of a 7μm polyolefin diaphragm by micro-concave coating. The diaphragm was placed in a constant temperature oven to dry at 60°C for 15 minutes. The final single-sided coated diaphragm was marked as 7+4P, and the double-sided coated diaphragm was marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0067] Example 5

[0068] The difference from Example 1 is that this embodiment uses potassium hydroxide solution in the process of etching the polyimide microspheres with alkaline solution. The other processes are the same as those in Example 1. The specific implementation steps are as follows:

[0069] (1) Preparation of polyimide composite microspheres with lithium dendrite inhibition function: Prepare polyamic acid of PMDA / ODA system, weigh the monomer pyromellitic anhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to the molar ratio of 1.01:1, first dissolve all ODA in solvent N,N-dimethylformamide (DMF), then add PMDA in batches, and react for 3 hours under 0℃ ice water bath conditions, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were placed in a sodium hydroxide solution for 10 minutes, wherein the concentration of the potassium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes after treatment, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in 3wt% acetic acid for 10 minutes, washed with deionized water for 5 minutes after treatment, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in a 0.2mol / L silver nitrate solution for 10 minutes, then washed with deionized water for 3 minutes, and then dried in a 60°C oven for 15 minutes. The polyimide microspheres loaded with silver ions on the surface were immersed in a 0.1mol / L DMAB solution for 15 minutes for reduction treatment to obtain polyimide composite microspheres loaded with silver nanocrystals on the shallow surface.

[0070] (2) Preparation of polyimide composite microsphere composition and coated diaphragm with lithium dendrite inhibition function: Weigh 200g microspheres, pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g hexadecyltrimethylammonium bromide powder, 4g sodium carboxymethyl cellulose, and 20g acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir with a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. The diaphragm coating adopts a micro-concave coating process, and the obtained polyimide composite microsphere composition is placed in a vacuum oven for defoaming treatment for 1h, and then evenly coated on one or both sides of a 7μm polyolefin diaphragm by micro-concave coating. The diaphragm was placed in a constant temperature oven to dry at 60°C for 15 minutes. The final single-sided coated diaphragm was marked as 7+4P, and the double-sided coated diaphragm was marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0071] Example 6

[0072] The difference from Example 1 is that this example uses formic acid solution in the acidification process of polyimide microspheres. The other processes are the same as those in Example 1. The specific implementation steps are as follows:

[0073] (1) Preparation of polyimide composite microspheres with lithium dendrite inhibition function: Prepare polyamic acid of PMDA / ODA system, weigh the monomer pyromellitic anhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to the molar ratio of 1.01:1, first dissolve all ODA in solvent N,N-dimethylformamide (DMF), then add PMDA in batches, and react for 3 hours under 0℃ ice water bath conditions, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were placed in a sodium hydroxide solution for 10 minutes, wherein the concentration of the potassium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in 3wt% formic acid for 10 minutes, washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in a 0.2mol / L silver nitrate solution for 10 minutes, then washed with deionized water for 3 minutes, and then dried in a 60°C oven for 15 minutes. The polyimide microspheres loaded with silver ions on the surface were immersed in a 0.1mol / L DMAB solution for 15 minutes for reduction treatment to obtain polyimide composite microspheres loaded with silver nanocrystals on the shallow surface.

[0074] (2) Preparation of polyimide composite microsphere composition and coated diaphragm with lithium dendrite inhibition function: Weigh 200g microspheres, pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g hexadecyltrimethylammonium bromide powder, 4g sodium carboxymethyl cellulose, and 20g acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir with a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. The diaphragm coating adopts a micro-concave coating process, and the obtained polyimide composite microsphere composition is placed in a vacuum oven for defoaming treatment for 1h, and then evenly coated on one or both sides of a 7μm polyolefin diaphragm by micro-concave coating. The diaphragm was placed in a constant temperature oven to dry at 60°C for 15 minutes. The final single-sided coated diaphragm was marked as 7+4P, and the double-sided coated diaphragm was marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0075] Example 7

[0076] Different from Embodiment 1, in this embodiment, when preparing polyimide composite microspheres with the function of inhibiting lithium dendrites, the concentration of the silver salt solution is adjusted. The other steps are the same as those in Embodiment 1. The specific implementation steps are as follows:

[0077] (1) Preparation of polyimide composite microspheres with lithium dendrite inhibition function: Prepare polyamic acid of PMDA / ODA system, weigh the monomer pyromellitic anhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to the molar ratio of 1.01:1, first dissolve all ODA in solvent N,N-dimethylformamide (DMF), then add PMDA in batches, and react for 3 hours under 0℃ ice water bath conditions, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were placed in a sodium hydroxide solution for 10 minutes, wherein the concentration of the sodium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in 3wt% acetic acid for 10 minutes, washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in a 0.4mol / L silver nitrate solution for 10 minutes, then washed with deionized water for 3 minutes, and then dried in a 60°C oven for 15 minutes. The polyimide microspheres loaded with silver ions on the surface were immersed in a 0.1mol / L DMAB solution for 15 minutes for reduction treatment to obtain polyimide composite microspheres loaded with silver nanocrystals on the shallow surface.

[0078] (2) Preparation of polyimide composite microsphere composition and coated diaphragm with lithium dendrite inhibition function: Weigh 200g microspheres, pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g hexadecyltrimethylammonium bromide powder, 4g sodium carboxymethyl cellulose, and 20g acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir with a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. The diaphragm coating adopts a micro-concave coating process, and the obtained polyimide composite microsphere composition is placed in a vacuum oven for defoaming treatment for 1h, and then evenly coated on one or both sides of a 7μm polyolefin diaphragm by micro-concave coating. The diaphragm was placed in a constant temperature oven to dry at 60°C for 15 minutes. The final single-sided coated diaphragm was marked as 7+4P, and the double-sided coated diaphragm was marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0079] Example 8

[0080] Different from Embodiment 1, in this embodiment, when preparing polyimide composite microspheres with the function of inhibiting lithium dendrites, the type of metal silver salt solution is adjusted, and the other steps are the same as those in Embodiment 1. The specific implementation steps are as follows:

[0081] (1) Preparation of polyimide composite microspheres with lithium dendrite inhibition function: Prepare polyamic acid of PMDA / ODA system, weigh the monomer pyromellitic anhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to the molar ratio of 1.01:1, first dissolve all ODA in solvent N,N-dimethylformamide (DMF), then add PMDA in batches, and react for 3 hours under 0℃ ice water bath conditions, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were placed in a sodium hydroxide solution for 10 minutes, wherein the concentration of the sodium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in 3wt% acetic acid for 10 minutes, washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in a silver ammonia solution with a silver ion concentration of 0.1 mol / L for 10 minutes, then washed with deionized water for 3 minutes, and then dried in a 60°C oven for 15 minutes. The polyimide microspheres with surface-loaded silver ions were immersed in a 0.1 mol / L DMAB solution for 15 minutes for reduction treatment to obtain polyimide composite microspheres with shallow surface-loaded silver nanocrystals.

[0082] (2) Preparation of polyimide composite microsphere composition and coated diaphragm with lithium dendrite inhibition function: Weigh 200g microspheres, pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g hexadecyltrimethylammonium bromide powder, 4g sodium carboxymethyl cellulose, and 20g acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir with a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. The diaphragm coating adopts a micro-concave coating process, and the obtained polyimide composite microsphere composition is placed in a vacuum oven for defoaming treatment for 1h, and then evenly coated on one or both sides of a 7μm polyolefin diaphragm by micro-concave coating. The diaphragm was placed in a constant temperature oven to dry at 60°C for 15 minutes. The final single-sided coated diaphragm was marked as 7+4P, and the double-sided coated diaphragm was marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0083] Example 9

[0084] A polyimide composite microsphere, composition and coated electrode having the function of inhibiting lithium dendrites, wherein the preparation method comprises the following steps:

[0085] (1) Preparation of polyimide composite microspheres with lithium dendrite inhibition function: Prepare polyamic acid of PMDA / ODA system, weigh the monomer pyromellitic anhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to the molar ratio of 1.01:1, first dissolve all ODA in solvent N,N-dimethylformamide (DMF), then add PMDA in batches, and react for 3 hours under 0℃ ice water bath conditions, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were placed in a sodium hydroxide solution for 10 minutes, wherein the concentration of the sodium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in 3wt% acetic acid for 10 minutes, washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in a 0.2mol / L silver nitrate solution for 10 minutes, then washed with deionized water for 3 minutes, and then dried in a 60°C oven for 15 minutes. The polyimide microspheres loaded with silver ions on the surface were immersed in a 0.1mol / L DMAB solution for 15 minutes for reduction treatment to obtain polyimide composite microspheres loaded with silver nanocrystals on the shallow surface.

[0086] (2) Preparation of polyimide composite microsphere composition and coated electrode with lithium dendrite inhibition function: Weigh 200g microspheres, pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g hexadecyltrimethylammonium bromide powder, 4g sodium carboxymethyl cellulose, and 20g acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir with a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. Electrode coating adopts a micro-concave coating process, put the obtained polyimide composite microsphere composition into a vacuum oven for defoaming treatment for 1h, and then use micro-concave coating to evenly coat one or both sides of a 7μm aluminum foil. After the pressing operation, the negative electrode is obtained, and the electrode is placed in a vacuum environment for drying. The drying temperature is 60°C and the drying time is 15 minutes. The final single-sided coated electrode is marked as 7+4P, and the double-sided coated electrode is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0087] Example 10

[0088] Different from Example 8, this example changes the chemical structure of polyimide, and uses hexafluorodianhydride (6FDA) with trifluoromethyl and 4,4'-biphenyl ether dianhydride (ODPA) monomers containing ether oxygen bonds. The other steps are the same as those of Example 8, and the specific implementation steps are as follows:

[0089] (1) Preparation of polyimide composite microspheres with lithium dendrite inhibition function: The monomer hexafluorodianhydride (6FDA), 4,4'-biphenyl ether dianhydride (ODPA) and the monomer 4,4'-diaminodiphenyl ether (ODA) were weighed in a ratio of 1.01:1, and the ODA was first completely dissolved in the solvent N,N-dimethylformamide (DMF), and then 6FDA was added in batches, and reacted in an ice-water bath at 0°C for 3 hours, and finally a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity was obtained. The solution was filled into a 10ml syringe and polyamic acid microspheres were obtained by electrostatic spraying, wherein the parameters of the spray device were: voltage 20kv, humidity 30%, temperature 25°C, and receiving distance 20cm. The microspheres were placed in a high-temperature hot furnace for imidization treatment, and the heating program was set as: heating from room temperature to 260°C at a heating rate of 3°C / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were placed in a sodium hydroxide solution for 10 minutes, wherein the concentration of the sodium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in 3wt% acetic acid for 10 minutes, washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in a 0.2mol / L silver nitrate solution for 10 minutes, washed with deionized water for 3 minutes, and then dried in a 60°C oven for 15 minutes. The polyimide microspheres loaded with silver ions on the surface were immersed in a 0.1mol / L DMAB solution for 15 minutes for reduction treatment to obtain polyimide composite microspheres loaded with silver nanocrystals on the shallow surface.

[0090] (2) Preparation of polyimide composite microsphere composition and coated electrode with lithium dendrite inhibition function: Weigh 200g microspheres, pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g hexadecyltrimethylammonium bromide powder, 4g sodium carboxymethyl cellulose, and 20g acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir with a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. Electrode coating adopts a micro-concave coating process, put the obtained polyimide composite microsphere composition into a vacuum oven for defoaming treatment for 1h, and then use micro-concave coating to evenly coat one or both sides of a 7μm aluminum foil. After the pressing operation, the negative electrode is obtained, and the electrode is placed in a vacuum environment for drying. The drying temperature is 60°C and the drying time is 15 minutes. The final single-sided coated electrode is marked as 7+4P, and the double-sided coated electrode is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0091] Embodiment 11

[0092] Different from Example 8, in this example, when preparing polyimide composite microspheres with the function of inhibiting lithium dendrites, the proportion of the metal silver salt solution is adjusted, and the other steps are the same as those in Example 8. The specific implementation steps are as follows:

[0093] (1) Preparation of polyimide composite microspheres with lithium dendrite inhibition function: Prepare polyamic acid of PMDA / ODA system, weigh the monomer pyromellitic anhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to the molar ratio of 1.01:1, first dissolve all ODA in solvent N,N-dimethylformamide (DMF), then add PMDA in batches, and react for 3 hours under 0℃ ice water bath conditions, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were placed in a sodium hydroxide solution for 10 minutes, wherein the concentration of the sodium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in 3wt% acetic acid for 10 minutes, washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in a 0.4mol / L silver nitrate solution for 10 minutes, then washed with deionized water for 3 minutes, and then dried in a 60°C oven for 15 minutes. The polyimide microspheres loaded with silver ions on the surface were immersed in a 0.1mol / L DMAB solution for 15 minutes for reduction treatment to obtain polyimide composite microspheres loaded with silver nanocrystals on the shallow surface.

[0094] (2) Preparation of polyimide composite microsphere composition and coated electrode with lithium dendrite inhibition function: Weigh 200g microspheres, pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g hexadecyltrimethylammonium bromide powder, 4g sodium carboxymethyl cellulose, and 20g acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir with a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. Electrode coating adopts a micro-concave coating process, put the obtained polyimide composite microsphere composition into a vacuum oven for defoaming treatment for 1h, and then use micro-concave coating to evenly coat one or both sides of a 7μm aluminum foil. After the pressing operation, the negative electrode is obtained, and the electrode is placed in a vacuum environment for drying. The drying temperature is 60°C and the drying time is 15 minutes. The final single-sided coated electrode is marked as 7+4P, and the double-sided coated electrode is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0095] Embodiment 11

[0096] Different from Example 8, in this example, when preparing polyimide composite microspheres with the function of inhibiting lithium dendrites, the type of metal silver salt solution is adjusted, and the other steps are the same as those of Example 8. The specific implementation steps are as follows:

[0097] (1) Preparation of polyimide composite microspheres with lithium dendrite inhibition function: Prepare polyamic acid of PMDA / ODA system, weigh the monomer pyromellitic anhydride (PMDA) and the monomer 4,4'-diaminodiphenyl ether (ODA) according to the molar ratio of 1.01:1, first dissolve all ODA in solvent N,N-dimethylformamide (DMF), then add PMDA in batches, and react for 3 hours under 0℃ ice water bath conditions, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were placed in a sodium hydroxide solution for 10 minutes, wherein the concentration of the sodium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in 3wt% acetic acid for 10 minutes, washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were placed in a silver ammonia solution with a silver ion concentration of 0.1 mol / L for 10 minutes, then washed with deionized water for 3 minutes, and then dried in a 60°C oven for 15 minutes. The polyimide microspheres with surface-loaded silver ions were immersed in a 0.1 mol / L DMAB solution for 15 minutes for reduction treatment to obtain polyimide composite microspheres with shallow surface-loaded silver nanocrystals.

[0098] (2) Preparation of polyimide composite microsphere composition and coated diaphragm with lithium dendrite inhibition function: Weigh 200g microspheres, pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g hexadecyltrimethylammonium bromide powder, 4g sodium carboxymethyl cellulose, and 20g acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir with a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. Electrode coating adopts a micro-concave coating process, put the obtained polyimide composite microsphere composition into a vacuum oven for defoaming treatment for 1h, and then use micro-concave coating to evenly coat one or both sides of a 7μm aluminum foil. After the pressing operation, the negative electrode is obtained, and the electrode is placed in a vacuum environment for drying. The drying temperature is 60°C and the drying time is 15 minutes. The final single-sided coated electrode is marked as 7+4P, and the double-sided coated electrode is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0099] Comparative Example 1

[0100] A polyimide microsphere composition and a coated diaphragm, wherein the preparation method thereof comprises the following steps:

[0101] (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 solvent N,N-dimethylformamide (DMF), then add PMDA in batches, react for 3 hours under ice-water bath at 0℃, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe, and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres.

[0102] (2) Preparation of polyimide microsphere composition and coated diaphragm: Weigh 200g of microspheres, pour into a mixed solvent of 395g of water and 5g of ethanol to obtain a polyimide microsphere dispersion, then weigh 2g of hexadecyltrimethylammonium bromide powder, 4g of sodium carboxymethylcellulose, and 20g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir using a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. The diaphragm coating adopts a micro-concave coating process, and the obtained polyimide microsphere composition is placed in a vacuum oven for defoaming treatment for 1h, and then evenly coated on one or both sides of a 7μm polyolefin diaphragm using a micro-concave coating method. The diaphragm was placed in a constant temperature oven to dry at 60°C for 15 minutes. The final single-sided coated diaphragm was marked as 7+4P, and the double-sided coated diaphragm was marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0103] Comparative Example 2

[0104] A polyimide microsphere composition and a coated diaphragm, wherein the preparation method thereof comprises the following steps:

[0105] (1) Preparation of polyimide microspheres: Prepare polyamic acid of BPDA / ODA system, weigh monomer 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and monomer 4,4'-diaminodiphenyl ether (ODA) according to the molar ratio of 1.01:1, first dissolve all ODA in solvent N,N-dimethylformamide (DMF), then add BPDA in batches, react for 3 hours under ice-water bath at 0℃, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe, and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres.

[0106] (2) Preparation of polyimide microsphere composition and coated diaphragm: Weigh 200g of microspheres, pour into a mixed solvent of 395g of water and 5g of ethanol to obtain a polyimide microsphere dispersion, then weigh 2g of hexadecyltrimethylammonium bromide powder, 4g of sodium carboxymethylcellulose, and 20g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir using a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. The diaphragm coating adopts a micro-concave coating process, and the obtained polyimide microsphere composition is placed in a vacuum oven for defoaming treatment for 1h, and then evenly coated on one or both sides of a 7μm polyolefin diaphragm using a micro-concave coating method. The diaphragm was placed in a constant temperature oven to dry at 60°C for 15 minutes. The final single-sided coated diaphragm was marked as 7+4P, and the double-sided coated diaphragm was marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0107] Comparative Example 3

[0108] A polyimide microsphere composition and a coated diaphragm, wherein the preparation method thereof comprises the following steps:

[0109] (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 solvent N,N-dimethylformamide (DMF), then add PMDA in batches, react for 3 hours under ice-water bath at 0℃, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe, and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were treated in a sodium hydroxide solution for 10 minutes, wherein the concentration of the potassium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were treated in 3wt% acetic acid for 10 minutes, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes.

[0110] (2) Preparation of polyimide microsphere composition and coated diaphragm: Weigh 200g of the microspheres prepared in step (1), pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g of hexadecyltrimethylammonium bromide powder, 4g of sodium carboxymethylcellulose, and 20g of acrylate adhesive with a solid content of 25%, successively add them to the polyimide microsphere dispersion, use a high-speed homogenizer to stir, set the speed to 8000r / min, and stir for 60min. The diaphragm coating adopts a micro-concave coating process, put the obtained polyimide microsphere composition into a vacuum oven for defoaming treatment, the treatment time is 1h, and then use the micro-concave coating method to evenly coat one or both sides of a 7μm polyolefin diaphragm. The diaphragm was placed in a constant temperature oven to dry at 60°C for 15 minutes. The final single-sided coated diaphragm was marked as 7+4P, and the double-sided coated diaphragm was marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0111] Comparative Example 4

[0112] A polyimide microsphere composition and a coated diaphragm, wherein the preparation method thereof comprises the following steps:

[0113] (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 solvent N,N-dimethylformamide (DMF), then add PMDA in batches, react for 3 hours under ice-water bath at 0℃, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe, and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were treated in a sodium hydroxide solution for 10 minutes, wherein the concentration of the potassium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were treated in 3wt% acetic acid for 10 minutes, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were treated in a 0.2 mol / L silver nitrate solution for 10 minutes, and then washed with deionized water for 3 minutes, and then dried in a 60°C oven for 15 minutes.

[0114] (2) Preparation of polyimide microsphere composition and coated diaphragm: Weigh 200g of the microspheres prepared in step (1), pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g of hexadecyltrimethylammonium bromide powder, 4g of sodium carboxymethylcellulose, and 20g of acrylate adhesive with a solid content of 25%, successively add them to the polyimide microsphere dispersion, use a high-speed homogenizer to stir, set the speed to 8000r / min, and stir for 60min. The diaphragm coating adopts a micro-concave coating process, put the obtained polyimide microsphere composition into a vacuum oven for defoaming treatment, the treatment time is 1h, and then use the micro-concave coating method to evenly coat one or both sides of a 7μm polyolefin diaphragm. The diaphragm was placed in a constant temperature oven to dry at 60°C for 15 minutes. The final single-sided coated diaphragm was marked as 7+4P, and the double-sided coated diaphragm was marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0115] Comparative Example 5

[0116] A polyimide microsphere composition and a coated electrode, wherein the preparation method comprises the following steps:

[0117] (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 solvent N,N-dimethylformamide (DMF), then add PMDA in batches, react for 3 hours under ice-water bath at 0℃, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe, and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres.

[0118] (2) Preparation of polyimide microsphere composition and coated electrode: Weigh 200g microspheres, pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g hexadecyltrimethylammonium bromide powder, 4g sodium carboxymethylcellulose, and 20g acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, and stir using a high-speed homogenizer, with the speed set at 8000r / min and the stirring time being 60min. Electrode coating adopts a micro-concave coating process, and the obtained polyimide microsphere composition is placed in a vacuum oven for defoaming treatment for 1h, and then evenly coated on one or both sides of a 7μm aluminum foil using a micro-concave coating method. After the pressing operation, the negative electrode is obtained, and the electrode is placed in a vacuum environment for drying. The drying temperature is 60°C and the drying time is 15 minutes. The final single-sided coated electrode is marked as 7+4P, and the double-sided coated electrode is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0119] Comparative Example 6

[0120] A polyimide microsphere composition and a coated electrode, wherein the preparation method comprises the following steps:

[0121] (1) Preparation of polyimide microspheres: Prepare polyamic acid of BPDA / ODA system, weigh monomer 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and monomer 4,4'-diaminodiphenyl ether (ODA) according to the molar ratio of 1.01:1, first dissolve all ODA in solvent N,N-dimethylformamide (DMF), then add BPDA in batches, react for 3 hours under ice-water bath at 0℃, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe, and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres.

[0122] (2) Preparation of polyimide microsphere composition and coated diaphragm: Weigh 200g of microspheres, pour into a mixed solvent of 395g of water and 5g of ethanol to obtain a polyimide microsphere dispersion, then weigh 2g of hexadecyltrimethylammonium bromide powder, 4g of sodium carboxymethylcellulose, and 20g of acrylate adhesive with a solid content of 25%, and add them to the polyimide microsphere dispersion in turn, stir using a high-speed homogenizer, set the speed to 8000r / min, and stir for 60min. Electrode coating adopts a micro-concave coating process, and the obtained polyimide microsphere composition is placed in a vacuum oven for defoaming treatment for 1h, and then evenly coated on one or both sides of a 7μm aluminum foil using a micro-concave coating method. After the pressing operation, the negative electrode is obtained, and the electrode is placed in a vacuum environment for drying. The drying temperature is 60°C and the drying time is 15 minutes. The final single-sided coated electrode is marked as 7+4P, and the double-sided coated electrode is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0123] Comparative Example 7

[0124] A polyimide microsphere composition and a coated electrode, wherein the preparation method comprises the following steps:

[0125] (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 solvent N,N-dimethylformamide (DMF), then add PMDA in batches, react for 3 hours under ice-water bath at 0℃, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe, and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were treated in a sodium hydroxide solution for 10 minutes, wherein the concentration of the potassium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were treated in 3wt% acetic acid for 10 minutes, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes.

[0126] (2) Preparation of polyimide microsphere composition and coated diaphragm: Weigh 200g of the microspheres prepared in step (1), pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g of hexadecyltrimethylammonium bromide powder, 4g of sodium carboxymethylcellulose, and 20g of acrylate adhesive with a solid content of 25%, successively add them to the polyimide microsphere dispersion, use a high-speed homogenizer to stir, set the speed to 8000r / min, and stir for 60min. Electrode coating adopts a micro-concave coating process, put the obtained polyimide microsphere composition into a vacuum oven for defoaming treatment, the treatment time is 1h, and then use a micro-concave coating method to evenly coat one or both sides of a 7μm aluminum foil. After the pressing operation, the negative electrode is obtained, and the electrode is placed in a vacuum environment for drying. The drying temperature is 60°C and the drying time is 15 minutes. The final single-sided coated electrode is marked as 7+4P, and the double-sided coated electrode is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0127] Comparative Example 8

[0128] A polyimide microsphere composition and a coated electrode, wherein the preparation method comprises the following steps:

[0129] (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 solvent N,N-dimethylformamide (DMF), then add PMDA in batches, react for 3 hours under ice-water bath at 0℃, and finally obtain a relatively clear and transparent polyamic acid solution with a solid content of 12wt% and moderate viscosity. The solution is loaded into a 10ml syringe, and polyamic acid microspheres are obtained by electrostatic spraying, wherein the parameters of the spray device are: voltage 20kv, humidity 30%, temperature 25℃, and receiving distance 20cm. The microspheres are placed in a high-temperature hot furnace for imidization treatment, and the heating program is set as: heating from room temperature to 260℃ at a heating rate of 3℃ / min, keeping warm for 30min and then naturally cooling to room temperature to obtain polyimide microspheres. The polyimide microspheres were treated in a sodium hydroxide solution for 10 minutes, wherein the concentration of the potassium hydroxide solution was 0.2 mol / L, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were treated in 3wt% acetic acid for 10 minutes, and then washed with deionized water for 5 minutes, and then dried in a 60°C oven for 15 minutes. The microspheres were treated in a 0.2 mol / L silver nitrate solution for 10 minutes, and then washed with deionized water for 3 minutes, and then dried in a 60°C oven for 15 minutes.

[0130] (2) Preparation of polyimide microsphere composition and coated diaphragm: Weigh 200g of the microspheres prepared in step (1), pour into a mixed solvent of 395g water and 5g ethanol to obtain a polyimide microsphere dispersion, then weigh 2g of hexadecyltrimethylammonium bromide powder, 4g of sodium carboxymethylcellulose, and 20g of acrylate adhesive with a solid content of 25%, successively add them to the polyimide microsphere dispersion, use a high-speed homogenizer to stir, set the speed to 8000r / min, and stir for 60min. Electrode coating adopts a micro-concave coating process, put the obtained polyimide microsphere composition into a vacuum oven for defoaming treatment, the treatment time is 1h, and then use a micro-concave coating method to evenly coat one or both sides of a 7μm aluminum foil. After the pressing operation, the negative electrode is obtained, and the electrode is placed in a vacuum environment for drying. The drying temperature is 60°C and the drying time is 15 minutes. The final single-sided coated electrode is marked as 7+4P, and the double-sided coated electrode is marked as 2P+7+2P, where the numbers "4" and "2" represent the coating thickness.

[0131] The above description is only a preferred embodiment of the present invention, and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A polyimide composite microsphere composition and coating having the function of inhibiting lithium dendrites, characterized in that: The composition is composed of polyimide composite microspheres, a binder, a surfactant, a dispersant and a solvent, wherein the polyimide composite microspheres are 5-59 parts, the binder is 0.1-10 parts, the surfactant is 0.01-3 parts, the dispersant is 0.01-8 parts and the solvent is 40-95 parts; the binder 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 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 bromide ammonium, dodecyltrimethylammonium bromide, dodecylpyridinium bromide, anionic surfactants, such as fatty acid salts, sulfonates, phosphates and sulfates, one or a combination of two or more; the dispersant is hydroxypropyl methylcellulose, hydroxyethyl cellulose, cellulose alkyl ether or cellulose hydroxyalkyl ether and other cellulose ether dispersants, polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, polyacrylamide, sodium polyacrylate, one or a combination of two or more; the solvent is an organic solvent or an aqueous solvent, the organic solvent is N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, one or a combination of two or more, the aqueous solvent is pure water or water and ethanol, ethylene glycol, propanol, glycerol, isopropanol, butanol, one or a combination of two or more; the coating is formed by coating the above composition and then drying.

2. The polyimide composite microsphere composition and coating for inhibiting lithium dendrites according to claim 1, characterized in that: The polyimide composite microspheres for inhibiting lithium dendrites are polyimide microspheres loaded with silver nanocrystals on the shallow surface. The particle size of the polyimide microspheres is 0.02 μm-10 μm, and the particle size of the silver nanocrystals is in the range of 0.01 μm-2 μm.

3. The polyimide composite microspheres with the function of inhibiting lithium dendrites and the preparation method according to claim 2 are characterized in that: Follow these steps: A: The polyamic acid solution is synthesized by a solution polycondensation method, wherein a diamine is dissolved in an organic solvent, a dibasic acid anhydride is added in batches, and the precursor solution (polyamic acid solution) is obtained by mechanical stirring in an ice water bath, and polyamic acid microspheres are prepared by an electrostatic spray method, a phase separation method, an emulsion evaporation method, or a spray drying method; B: subjecting the polyamic acid microspheres to a high temperature heat treatment to cause the polyamic acid to undergo a thermal imidization reaction to obtain polyimide microspheres; C: placing the microspheres obtained in step B in an alkaline solution of a certain concentration, stirring or ultrasonically treating, and maintaining the solution for a certain period of time, so that the imide rings on the surface of the polyimide microspheres undergo alkaline hydrolysis and ring opening; D: washing the microspheres obtained in step C with deionized water and drying, then immersing them in an acidic solution of a certain concentration for acidification, stirring or ultrasonic treatment, and washing with deionized water to obtain polyimide microspheres containing carboxyl groups on the surface; E: placing the microspheres obtained in step D in a soluble silver salt solution of a certain concentration for treatment, complexing the silver ions to the surface of the microspheres through an ion exchange reaction, washing with deionized water and drying, and finally obtaining polyimide microspheres with silver ions loaded on the surface; F: The polyimide microspheres with surface loaded silver ions obtained in step E are subjected to reduction treatment to obtain polyimide microspheres with surface silver.

4. The polyimide composite microspheres for inhibiting lithium dendrites and the preparation method according to claim 3, characterized in that: The polyimide described in step A is any polyimide prepared by solution condensation polymerization of polyacid anhydride and polyamine, and the solid content of polyamic acid is 10-40wt%; the organic solvent is any one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

5. The polyimide composite microspheres for inhibiting lithium dendrites and the preparation method thereof according to claim 3, characterized in that: The high temperature heat treatment described in step B has a treatment temperature of 260-300° C. and a treatment time of 0.5-1 h.

6. The polyimide composite microspheres for inhibiting lithium dendrites and the preparation method thereof according to claim 3, characterized in that: The alkaline solution described in step C is any one of sodium hydroxide, lithium hydroxide and potassium hydroxide, with a concentration of 0.01-5 mol / L, and the stirring or ultrasonic treatment time is 5-45 min.

7. The polyimide composite microspheres for inhibiting lithium dendrites and the preparation method thereof according to claim 3, characterized in that: The deionized water washing time in step D is 3-10 minutes, the drying temperature is 40-70°C, and the drying time is 10-100 minutes; the acidic solution is any one of formic acid, acetic acid, hydrochloric acid, and sulfuric acid, with a concentration of 1-30wt%, and the stirring or ultrasonic treatment time is 5-45 minutes.

8. The polyimide composite microspheres for inhibiting lithium dendrites and the preparation method thereof according to claim 3, characterized in that: The metal silver salt solution described in step E is one or more of an aqueous solution of silver nitrate, silver fluoride, silver acetate, silver fluoroborate, silver benzoate, silver perchlorate, silver trifluoromethanesulfonate, and a silver ammonia solution. The concentration of the metal silver salt solution is 0.1-1.5 mol / L, and the treatment time is 5-45 min. The deionized water is used for washing for 3-10 min, the drying temperature is 40-70° C., and the drying time is 10-100 min.

9. The polyimide composite microspheres for inhibiting lithium dendrites and the preparation method thereof according to claim 3, characterized in that: In step F, the reduction treatment of silver ions is chemical reduction or thermal reduction, and the reducing agent used in the chemical reduction is one or more of dimethylamine borane (DMAB) solution, hydrazine hydrate solution, alkaline glucose solution and ascorbic acid solution, with a concentration of 0.01-0.2 mol / L, and the reduction time is 5-60 min; The temperature used for thermal reduction is 290-310°C, and the reduction time is 1-8h.

10. A polyimide composite microsphere composition coated separator having the function of inhibiting lithium dendrites, characterized in that: The coated diaphragm is obtained by coating the composition of polyimide composite microspheres in claim 1 on at least one side of the porous membrane, and the single-sided coating thickness is 1-20 μm; the porous base membrane is one of a polyolefin diaphragm, a cellulose diaphragm, a polyester diaphragm, a nanofiber non-woven diaphragm, and an aramid diaphragm; the method of coating the diaphragm is one of micro-concave coating, extrusion coating, transfer coating, dip coating, and wire rod coating.

11. A polyimide composite microsphere composition coated electrode having the function of inhibiting lithium dendrites, characterized in that: The coated electrode is obtained by coating the composition of polyimide composite microspheres in claim 1 on at least one side of the surface of the electrode negative electrode sheet, and the single-sided coating thickness is 1-20 μm; the electrode coating method is one of micro-concave coating, extrusion coating, transfer coating, dip coating, and wire rod coating.

12. A lithium ion battery, characterized in that: The lithium ion battery comprises a positive electrode, a negative electrode, an electrolyte, and a separator according to claim 10 arranged between the positive electrode and the negative electrode.

13. A lithium ion battery, characterized in that: The lithium-ion battery consists of a positive electrode, a separator, an electrolyte and a negative electrode sheet according to claim 11.

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