Cathode material of branched porous polyimide / MXene / polypyrrole composite coating layer with double conductive mechanisms, preparation method and lithium battery

Abstract

The invention discloses a positive electrode material of a branched porous polyimide / MXene / polypyrrole composite coating layer with a double-conductive mechanism and a preparation method, and the positive electrode material comprises the branched porous polyimide / MXene / polypyrrole composite coating layer with the double-conductive mechanism, which is prepared by a wet chemical deposition method and an in-situ polymerization method. The composite coating layer combines excellent thermal stability and chemical stability of polyimide, high specific surface area and high porosity characteristics of the branched porous PI / MXene structure, rapid lithium ion channels and good conductivity of the conductive polymer. By synergistically constructing an interface functional composite coating layer of a double-conductive mechanism, the transmission efficiency of lithium ions and electrons can be improved, the interface side reaction between an electrolyte and a positive active material is reduced, the interface stability is improved, the degradation rate of an electrode material structure is reduced, and the stability and the service life of the battery in a long-cycle process are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a cathode material with a branched porous polyimide / MXene / polypyrrole composite coating layer having a double conduction mechanism, a preparation method and a lithium battery. BACKGROUND

[0002] Lithium ion batteries are widely used in electronic devices and electric vehicles due to their high efficiency and light weight, but the improvement of energy density also brings serious safety hazards, especially the problem of thermal runaway. High-nickel NCM811 cathode materials have the advantages of high capacity and energy density, but they have poor thermal stability and fast capacity decay. The main problems include cation mixing, side reactions between electrolyte and electrode, etc. To improve their performance, methods such as surface coating, bulk doping and microstructure modification are often used. For the modification strategy of coating, traditional coating materials such as oxides and fluorides have problems such as uneven coating, poor mechanical properties, high cost, etc.

[0003] Based on the above problems, the present application innovatively proposes a battery cathode material with a branched porous polyimide / MXene / polypyrrole composite coating layer having a double conduction mechanism. This design combines the excellent thermal and chemical stability of polyimide, the high specific surface area and high porosity characteristics of the branched porous PI / MXene structure, the fast lithium ion channel, and the good conductivity of the conductive polymer. By modifying the surface of the cathode material with a composite coating, the structure of the cathode material is stabilized, the interface side reaction is inhibited, and the cycle stability and safety of the lithium battery are improved. SUMMARY

[0004] The present application aims to provide a battery cathode material with a branched porous polyimide / MXene / polypyrrole composite coating layer having a double conduction mechanism, a preparation method and a lithium battery assembled using the cathode material. The composite coating layer combines the excellent thermal and chemical stability of polyimide, the high specific surface area and high porosity characteristics of the branched porous PI / MXene structure, the fast lithium ion channel, and the good conductivity of the conductive polymer, effectively improving the interface stability and structural integrity of the cathode material, improving the lithium ion transmission rate, and significantly inhibiting the electrolyte interface side reaction and the degradation of the cathode material structure. The composite coated cathode material is applied to a lithium battery, which not only improves the rate performance and capacity retention of the battery, but also enhances its high-temperature safety and long cycle stability.

[0005] The application provides a lithium ion battery positive electrode material with a branched porous polyimide / MXene / polypyrrole composite coating layer having a double conductive mechanism and a preparation method.

[0006] A positive electrode material with a branched porous polyimide / MXene / polypyrrole composite coating layer having a double conductive mechanism and a preparation method, characterized in that the following steps are included:

[0007] A: A polyamide acid solution is synthesized by a solution polycondensation method, a polyamine is dissolved in an organic solvent, a polybasic anhydride is added in batches, and a precursor solution (polyamide acid solution) is obtained by mechanical stirring in an ice water bath.

[0008] B: LiF is mixed with a hydrochloric acid solution in a beaker at a certain temperature, then Ti3AlC2 powder is slowly added to the above solution to avoid releasing a large amount of heat, after stirring for a period of time, the obtained multi-layer MXene is centrifuged, washed repeatedly with deionized water, and freeze-dried, then continue stirring for a period of time, then the treated multi-layer MXene is centrifuged to obtain a precipitate, then the obtained black powder is dispersed in water and ultrasonicated in an argon environment, finally, the mixed solution is centrifuged at a speed, the filtrate is collected and freeze-dried to obtain few-layer MXene.

[0009] C: The last prepared MXene in B is added to the PAA solution prepared in A, stirred uniformly to obtain a PAA / MXene solution, then the PAA / MXene solution is mixed uniformly with a positive electrode active material, and further thermal imidization treatment is carried out in a high-temperature oven to obtain a branched porous PI / MXene coated positive electrode active material, the coating method adopted is a wet chemical deposition method, and the coating thickness is 1-3 nm.

[0010] D: The branched porous PI / MXene coated positive electrode active material obtained in C is subjected to in-situ polymerization to cover a polypyrrole layer, which is realized as follows: pyrrole monomers and the original positive electrode active material with a branched porous PI / MXene coating layer are added to anhydrous ethanol and stirred thoroughly, then monomers and sodium p-toluenesulfonate are added to the above mixture, next, FeCl3·6H2O is dissolved in anhydrous ethanol and added to the solution, then the mixture is thoroughly stirred and uniformly under an ice water bath, after complete reaction, the mixture is filtered and washed, dried under vacuum, and then a positive electrode active material with a branched porous PI / MXene / conductive polymer composite coating layer is obtained.

[0011] Further, the polyimide mentioned in step A is any polyimide prepared by solution condensation polymerization of a polyacid anhydride and a polyamine, wherein the diacid anhydride is selected from 4,4'-(hexafluoroisopropene) phthalic anhydride (6FDA), pyromellitic dianhydride (PMDA), biphenyl dianhydride (BPDA), 4,4'-diphenyl ether dianhydride (ODPA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenyl sulfone tetracarboxylic dianhydride (DSDA), 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA), 1 The polyamine is selected from one or more of 4,4'-diaminodiphenyl sulfone (DDS), 4,4'-diaminodiphenyl ether (ODA), aminopropyl-terminated polydimethylsiloxane (DMS), 3,5'-diaminobenzoic acid (DABA), m-phenylenediamine (mPDA), p-phenylenediamine (p-PDA), 1,3,5-tris(4-aminophenyl)benzene (TAPB), 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), and 3,6-diaminocarbazole (DAC).

[0012] Further, the organic solvent mentioned in step A is one or a combination of two or more of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc).

[0013] Further, in step B, take 3-5 parts of LiF and 3-5 parts of hydrochloric acid, mix them at 40-50℃, take 1-2 parts of Ti3AlC2 powder, stir for 40-48 hours, freeze dry for 20-24 hours, continue stirring at 40-50℃ for 12-14 hours, start centrifugation speed at 8000-9000 r / min, disperse in 80-100 ml of water, sonicate for 2-2.5 hours, and finally centrifuge at 3500-4000 r / min.

[0014] Further, 2-3 parts of the MXene obtained in step C are added to 20-50 parts of PAA solution and stirred for 2-2.5 hours. The vacuum oven drying temperature is 50-70℃. The positive electrode active material includes one or more of the following materials: lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based positive electrode material, lithium manganese oxide, high-voltage spinel lithium nickel manganese oxide, lithium manganese phosphate, lithium cobalt phosphate, lithium nickel phosphate, lithium-rich layered oxide, etc. The coating method is wet chemical deposition, the coating thickness is 1-3 nm, the solid content of the polyamic acid solution is 10%-20%, and the high-temperature thermal imidization procedure is as follows: first, heat to the pre-imidization temperature of 135-140℃ at 2-2.5℃ / min and hold for 30-40 min, and then continue to heat to 295-300℃ at 2-2.5℃ / min and hold for 60-70 min.

[0015] Further, in step D, the pyrrole monomer selected is 0.5-3 wt%, the molar ratio of monomer to sodium p-toluenesulfonate is 3:1, wherein sodium p-toluenesulfonate is added to the above mixture as a dopant, the molar ratio of monomer to FeCl3·6H2O is 1:1, the coating method is in-situ polymerization, the coating thickness is 1-3 nm, the subsequent stirring time is 2-3 h, the vacuum drying temperature is 50-60 °C, and the drying time is 10-12 h.

[0016] A lithium battery is characterized in that the positive electrode of the battery has a branched porous polyimide / MXene / polypyrrole composite coating layer with a dual conductivity mechanism, which is prepared by wet chemical deposition and in-situ polymerization.

[0017] The beneficial effects of this invention are as follows:

[0018] (1) The present invention provides a branched porous PI / MXene / polypyrrole composite coating material for lithium-ion batteries with a dual conductivity mechanism. In this material, polyimide can effectively maintain the structural integrity of the coating layer at high temperatures due to its excellent thermal and chemical stability. Furthermore, the porous structure of PI / MXene can increase the specific surface area and porosity, thereby increasing the lithium-ion transport rate. At the same time, the typical conductive polymer can effectively improve the electron transport efficiency of the cathode material surface and its current collector, constructing a continuous electron channel, thereby improving the overall electronic conductivity and rate performance of the electrode.

[0019] (2) The branched porous PI / MXene / polypyrrole composite coating lithium-ion battery cathode material with a dual conductivity mechanism provided by this invention exhibits excellent chemical stability and corrosion resistance to the electrolyte. This composite coating effectively suppresses side reactions between the cathode active material and the electrolyte, significantly improving interface stability. This interface protection effect helps reduce the degradation rate of the electrode material structure, thereby enhancing the stability and lifespan of the battery during long-cycle operation.

[0020] (3) The present invention provides a branched porous PI / MXene / polypyrrole composite coating material with dual conductivity mechanism. The composite coating significantly improves the interface stability and electrochemical performance of the cathode material by synergistically constructing an interface functionalized composite coating with dual conductivity mechanism. Attached Figure Description

[0021] Figure 1 SEM morphology of the positive electrode active material with a branched porous polyimide / MXene / polypyrrole composite coating layer for dual conductivity mechanism (Example 1);

[0022] Figure 2 TEM image of the positive electrode active material with a branched porous polyimide / MXene / polypyrrole composite coating layer for dual conductivity mechanism (Example 1);

[0023] Figure 3 SEM morphology of the uncoated positive electrode active material (Comparative Example 1);

[0024] Figure 4 SEM image of the positive electrode active material after 100 cycles of cycling with a branched porous polyimide / MXene / polypyrrole composite coating layer with dual conductivity mechanism (Example 1);

[0025] Figure 5 SEM morphology of the uncoated positive electrode active material after 100 cycles (Comparative Example 1); Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The following specific embodiments further illustrate the point. It should be noted that the following embodiments are only used to illustrate and not limit the technical solutions described in this invention. All equivalent substitutions made based on the technical solutions of this application fall within the protection scope of this invention.

[0028] Example 1

[0029] A method for preparing a branched porous polyimide / MXene / polypyrrole composite coating material for lithium-ion batteries with a dual conductivity mechanism includes the following steps:

[0030] (1) Preparation of polyamic acid precursor for polyimide coating: The solid content of the PAA solution was set to 15%. N-methylpyrrolidone (NMP) was used as the solvent. The polyamic acid precursor solution for polyimide was prepared using a synthesis system of 1,4,5,8-naphthalenetetracarboxylic anhydride (NTCDA), p-phenylenediamine (p-PDA), and 1,3,5-tris(4-aminophenyl)benzene (TAPB). The molar ratio of total anhydride groups to total amino groups was 1.01:1, and the molar amount of triamine TAPB accounted for 2% of the total molar amount of monomers. 3.894 g of NTCDA, 1.570 g of p-PDA, and 0.200 g of TAPB were weighed and set aside. 20 ml of NMP solution was added to a three-necked flask, followed by 1.570 g of p-PDA and 0.200 g of TAPB. The solid reagents were allowed to dissolve. Turn on the electric stirrer and wait for p-PDA and TAPB to completely dissolve in NMP solvent under mechanical stirring, then connect to an ice-water bath. Next, add NTCDA in batches, completing the addition after approximately 1 hour. After the addition is complete, rinse the volumetric flask with the remaining 10 ml of NMP solution and slowly add the solution along the wall of the three-necked flask. Continue stirring until the solution viscosity increases. Once the "climbing rod effect" is observed, continue stirring for approximately 3 hours to prepare the polyamic acid precursor solution for polyimide.

[0031] (2) Preparation of branched porous PI / MXene-coated positive electrode active material: 3-5 parts of LiF and 3-5 parts of hydrochloric acid solution were mixed in a beaker at 40-50℃. Then, 1-2 parts of Ti3AlC2 powder were slowly added to the solution to avoid releasing a large amount of heat. After stirring for 40-48 hours, the resulting multilayer MXene was centrifuged, washed repeatedly with deionized water, and freeze-dried for 20-24 hours. Then, it was stirred again at 40-50℃ for 12-14 hours. Then, the treated MXene was centrifuged at 8000-9000 r / min to obtain a precipitate. Subsequently, the obtained black powder was dispersed in 80-100 mL of water and sonicated under argon atmosphere for 2-2.5 hours. Finally, the mixed solution was centrifuged at 3500-4000 r / min, the filtrate was collected, and it was freeze-dried to obtain multilayer MXene. Two parts of the prepared MXene were added to 20 parts of the prepared PAA solution and stirred for 2-2.5 hours. Then, the PAA / MXene solution was mixed evenly with the positive electrode active material and further thermal imidization was carried out in a high-temperature oven to obtain a branched porous PI / MXene-coated positive electrode active material.

[0032] (3) Preparation of a branched porous PI / MXene / polypyrrole composite coating positive electrode active material with a dual conductivity mechanism and assembly of a lithium-ion battery: The positive electrode active material with a porous PI / MXene coating obtained above was subjected to in-situ polymerization to cover a polypyrrole layer, as follows: 0.5 wt% of pyrrole monomer and the original positive electrode active material with a branched porous PI / MXene coating were added to anhydrous ethanol and stirred thoroughly for 2-3 h. Then, it was added to the above mixture at a molar ratio (pyrrole monomer: sodium p-toluenesulfonate = 3:1), wherein sodium p-toluenesulfonate was added to the above mixture as a dopant. Next, FeCl3·6H2O was dissolved in anhydrous ethanol and added to the solution at a molar ratio (pyrrole monomer: FeCl3·6H2O = 1:1). Then, the mixture was stirred thoroughly in an ice-water bath. After complete reaction, the mixture was filtered and washed. The cathode material with a branched porous PI / MXene / polypyrrole composite coating layer and a dual conductivity mechanism was obtained by drying under vacuum at 50-60℃ for 10-12 hours. The coated cathode material, conductive carbon black, and PVDF were weighed at a mass ratio of 8:1:1, mixed, and NMP solvent was added to adjust the viscosity. The mixture was then stirred at a constant temperature and speed using a magnetic stirrer for 5-6 hours to ensure homogeneity. 2-3 ml of the cathode slurry was then dropped onto carbon-containing aluminum foil using a dropper, and uniformly coated using a 100 μm scraper. The mixture was then placed in a constant temperature oven at 60-70℃ for 3-4 hours to remove the solvent. The dried current collector was cut into 12 μm circular electrodes using an electrode punching machine, and then rolled using a roller press. The above steps successfully produced a positive electrode coated with polyimide. The lithium-ion button cell was assembled in an argon-filled glove box. The selected separator was a Celgard-2400, cut into 25μm discs using a cutting machine for later use. The electrolyte contained 1 mol / L... -1 A solution of DMC / EC / EMC (volume ratio 1:1:1) was prepared, and lithium sheet was used as the negative electrode.

[0033] Following the electrode preparation and battery assembly and testing methods described above, the lithium-ion battery assembled using this system exhibits a 0.1C discharge specific capacity of 196.37 mAh / g, an initial efficiency of 86.9%, and a capacity retention rate of 87.62% after 100 cycles at 0.1C.

[0034] Example 2

[0035] Unlike Example 1, this embodiment adjusts the proportion of MXene in the preparation of the composite-coated positive electrode active material. The other steps are the same as in Example 1. The specific implementation steps are as follows:

[0036] (1) Preparation of polyamic acid precursor for polyimide coating: The solid content of the PAA solution was set to 15%. N-methylpyrrolidone (NMP) was used as the solvent. The polyamic acid precursor solution for polyimide was prepared using a synthesis system of 1,4,5,8-naphthalenetetracarboxylic anhydride (NTCDA), p-phenylenediamine (p-PDA), and 1,3,5-tris(4-aminophenyl)benzene (TAPB). The molar ratio of total anhydride groups to total amino groups was 1.01:1, and the molar amount of triamine TAPB accounted for 2% of the total molar amount of monomers. 3.894 g of NTCDA, 1.570 g of p-PDA, and 0.200 g of TAPB were weighed and set aside. 20 ml of NMP solution was added to a three-necked flask, followed by 1.570 g of p-PDA and 0.200 g of TAPB. The solid reagents were allowed to dissolve. Turn on the electric stirrer and wait for p-PDA and TAPB to completely dissolve in NMP solvent under mechanical stirring, then connect to an ice-water bath. Next, add NTCDA in batches, completing the addition after approximately 1 hour. After the addition is complete, rinse the volumetric flask with the remaining 10 ml of NMP solution and slowly add the solution along the wall of the three-necked flask. Continue stirring until the solution viscosity increases. Once the "climbing rod effect" is observed, continue stirring for approximately 3 hours to prepare the polyamic acid precursor solution for polyimide.

[0037] (2) Preparation of branched porous PI / MXene-coated positive electrode active material: 3-5 parts of LiF and 3-5 parts of hydrochloric acid solution were mixed in a beaker at 40-50℃. Then, 1-2 parts of Ti3AlC2 powder were slowly added to the solution to avoid releasing a large amount of heat. After stirring for 40-48 hours, the resulting multilayer MXene was centrifuged, washed repeatedly with deionized water, and freeze-dried for 20-24 hours. Then, it was stirred again at 40-50℃ for 12-14 hours. Then, the treated MXene was centrifuged at 8000-9000 r / min to obtain a precipitate. Subsequently, the obtained black powder was dispersed in 80-100 mL of water and sonicated under argon atmosphere for 2-2.5 hours. Finally, the mixed solution was centrifuged at 3500-4000 r / min, the filtrate was collected, and it was freeze-dried to obtain multilayer MXene. Three parts of the prepared MXene were added to 20 parts of the prepared PAA solution and stirred for 2-2.5 hours. Then, the PAA / MXene solution was mixed evenly with the positive electrode active material and further thermal imidization was carried out in a high-temperature oven to obtain a branched porous PI / MXene-coated positive electrode active material.

[0038] (3) Preparation of a branched porous PI / MXene / polypyrrole composite coating positive electrode active material with a dual conductivity mechanism and assembly of a lithium-ion battery: The positive electrode active material with a porous PI / MXene coating obtained above was subjected to in-situ polymerization to cover a polypyrrole layer, as follows: 0.5 wt% of pyrrole monomer and the original positive electrode active material with a branched porous PI / MXene coating were added to anhydrous ethanol and stirred thoroughly for 2-3 h. Then, it was added to the above mixture at a molar ratio (pyrrole monomer: sodium p-toluenesulfonate = 3:1), wherein sodium p-toluenesulfonate was added to the above mixture as a dopant. Next, FeCl3·6H2O was dissolved in anhydrous ethanol and added to the solution at a molar ratio (pyrrole monomer: FeCl3·6H2O = 1:1). Then, the mixture was stirred thoroughly in an ice-water bath. After complete reaction, the mixture was filtered and washed. The cathode material with a branched porous PI / MXene / polypyrrole composite coating layer and a dual conductivity mechanism was obtained by drying under vacuum at 50-60℃ for 10-12 hours. The coated cathode material, conductive carbon black, and PVDF were weighed at a mass ratio of 8:1:1, mixed, and NMP solvent was added to adjust the viscosity. The mixture was then stirred at a constant temperature and speed using a magnetic stirrer for 5-6 hours to ensure homogeneity. 2-3 ml of the cathode slurry was then dropped onto carbon-containing aluminum foil using a dropper, and uniformly coated using a 100 μm scraper. The mixture was then placed in a constant temperature oven at 60-70℃ for 3-4 hours to remove the solvent. The dried current collector was cut into 12 μm circular electrodes using an electrode punching machine, and then rolled using a roller press. The above steps successfully produced a positive electrode coated with polyimide. The lithium-ion button cell was assembled in an argon-filled glove box. The selected separator was a Celgard-2400, cut into 25μm discs using a cutting machine for later use. The electrolyte contained 1 mol / L... -1 A solution of DMC / EC / EMC (volume ratio 1:1:1) was prepared, and lithium sheet was used as the negative electrode.

[0039] Following the electrode preparation and battery assembly and testing methods described above, the lithium-ion battery assembled by this system has a 0.1C discharge specific capacity of 197.23 mAh / g, an initial efficiency of 87.43%, and a capacity retention rate of 87.7% after 100 cycles at 0.1C.

[0040] Example 3

[0041] Unlike Embodiment 1, this embodiment adjusts the ratio of coated positive electrode material, binder, and conductive carbon black in the subsequent electrode preparation when preparing the composite-coated positive electrode active material. Other steps are the same as in Embodiment 1. The specific implementation steps are as follows:

[0042] (1) Preparation of polyamic acid precursor for polyimide coating: The solid content of the PAA solution was set to 15%. N-methylpyrrolidone (NMP) was used as the solvent. The polyamic acid precursor solution for polyimide was prepared using a synthesis system of 1,4,5,8-naphthalenetetracarboxylic anhydride (NTCDA), p-phenylenediamine (p-PDA), and 1,3,5-tris(4-aminophenyl)benzene (TAPB). The molar ratio of total anhydride groups to total amino groups was 1.01:1, and the molar amount of triamine TAPB accounted for 2% of the total molar amount of monomers. 3.894 g of NTCDA, 1.570 g of p-PDA, and 0.200 g of TAPB were weighed and set aside. 20 ml of NMP solution was added to a three-necked flask, followed by 1.570 g of p-PDA and 0.200 g of TAPB. The solid reagents were allowed to dissolve. Turn on the electric stirrer and wait for p-PDA and TAPB to completely dissolve in NMP solvent under mechanical stirring, then connect to an ice-water bath. Next, add NTCDA in batches, completing the addition after approximately 1 hour. After the addition is complete, rinse the volumetric flask with the remaining 10 ml of NMP solution and slowly add the solution along the wall of the three-necked flask. Continue stirring until the solution viscosity increases. Once the "climbing rod effect" is observed, continue stirring for approximately 3 hours to prepare the polyamic acid precursor solution for polyimide.

[0043] (2) Preparation of branched porous PI / MXene-coated positive electrode active material: 3-5 parts of LiF and 3-5 parts of hydrochloric acid solution were mixed in a beaker at 40-50℃. Then, 1-2 parts of Ti3AlC2 powder were slowly added to the solution to avoid releasing a large amount of heat. After stirring for 40-48 hours, the resulting multilayer MXene was centrifuged, washed repeatedly with deionized water, and freeze-dried for 20-24 hours. Then, it was stirred again at 40-50℃ for 12-14 hours. Then, the treated MXene was centrifuged at 8000-9000 r / min to obtain a precipitate. Subsequently, the obtained black powder was dispersed in 80-100 mL of water and sonicated under argon atmosphere for 2-2.5 hours. Finally, the mixed solution was centrifuged at 3500-4000 r / min, the filtrate was collected, and it was freeze-dried to obtain multilayer MXene. Two parts of the prepared MXene were added to 20 parts of the prepared PAA solution and stirred for 2-2.5 hours. Then, the PAA / MXene solution was mixed evenly with the positive electrode active material and further thermal imidization was carried out in a high-temperature oven to obtain a branched porous PI / MXene-coated positive electrode active material.

[0044] (3) Preparation of a branched porous PI / MXene / polypyrrole composite coating positive electrode active material with a dual conductivity mechanism and assembly of a lithium-ion battery: The positive electrode active material with a porous PI / MXene coating obtained above was subjected to in-situ polymerization to cover a polypyrrole layer, as follows: 0.5 wt% of pyrrole monomer and the original positive electrode active material with a branched porous PI / MXene coating were added to anhydrous ethanol and stirred thoroughly for 2-3 h. Then, it was added to the above mixture at a molar ratio (pyrrole monomer: sodium p-toluenesulfonate = 3:1), wherein sodium p-toluenesulfonate was added to the above mixture as a dopant. Next, FeCl3·6H2O was dissolved in anhydrous ethanol and added to the solution at a molar ratio (pyrrole monomer: FeCl3·6H2O = 1:1). Then, the mixture was stirred thoroughly in an ice-water bath. After complete reaction, the mixture was filtered and washed. The cathode material with a branched porous PI / MXene / polypyrrole composite coating layer and a dual conductivity mechanism was obtained by drying under vacuum at 50-60℃ for 10-12 hours. The coated cathode material, conductive carbon black, and PVDF were weighed at a mass ratio of 92:5:3, mixed, and NMP solvent was added to adjust the viscosity. The mixture was then stirred at a constant temperature and speed using a magnetic stirrer for 5-6 hours to ensure homogeneity. 2-3 ml of the cathode slurry was then dropped onto carbon-containing aluminum foil using a dropper, and uniformly coated using a 100 μm scraper. The mixture was then placed in a constant temperature oven at 60-70℃ for 3-4 hours to remove the solvent. The dried current collector was cut into 12 μm circular electrodes using an electrode punching machine, and then rolled using a roller press. The above steps successfully produced a positive electrode coated with polyimide. The lithium-ion button cell was assembled in an argon-filled glove box. The selected separator was a Celgard-2400, cut into 25μm discs using a cutting machine for later use. The electrolyte contained 1 mol / L... -1 A solution of DMC / EC / EMC (volume ratio 1:1:1) was prepared, and lithium sheet was used as the negative electrode.

[0045] Following the electrode preparation and battery assembly and testing methods described above, the lithium-ion battery assembled using this system exhibits a 0.1C discharge specific capacity of 198.34 mAh / g, an initial efficiency of 87.79%, and a capacity retention rate of 88.45% after 100 cycles at 0.1C.

[0046] Example 4

[0047] Unlike Embodiment 1, this embodiment adjusts the proportion of the polypyrrole coating layer when preparing the composite-coated positive electrode active material. The other steps are the same as in Embodiment 1. The specific implementation steps are as follows:

[0048] (1) Preparation of polyamic acid precursor for polyimide coating: The solid content of the PAA solution was set to 15%. N-methylpyrrolidone (NMP) was used as the solvent. The polyamic acid precursor solution for polyimide was prepared using a synthesis system of 1,4,5,8-naphthalenetetracarboxylic anhydride (NTCDA), p-phenylenediamine (p-PDA), and 1,3,5-tris(4-aminophenyl)benzene (TAPB). The molar ratio of total anhydride groups to total amino groups was 1.01:1, and the molar amount of triamine TAPB accounted for 2% of the total molar amount of monomers. 3.894 g of NTCDA, 1.570 g of p-PDA, and 0.200 g of TAPB were weighed and set aside. 20 ml of NMP solution was added to a three-necked flask, followed by 1.570 g of p-PDA and 0.200 g of TAPB. The solid reagents were allowed to dissolve. Turn on the electric stirrer and wait for p-PDA and TAPB to completely dissolve in NMP solvent under mechanical stirring, then connect to an ice-water bath. Next, add NTCDA in batches, completing the addition after approximately 1 hour. After the addition is complete, rinse the volumetric flask with the remaining 10 ml of NMP solution and slowly add the solution along the wall of the three-necked flask. Continue stirring until the solution viscosity increases. Once the "climbing rod effect" is observed, continue stirring for approximately 3 hours to prepare the polyamic acid precursor solution for polyimide.

[0049] (2) Preparation of branched porous PI / MXene-coated positive electrode active material: 3-5 parts of LiF and 3-5 parts of hydrochloric acid solution were mixed in a beaker at 40-50℃. Then, 1-2 parts of Ti3AlC2 powder were slowly added to the solution to avoid releasing a large amount of heat. After stirring for 40-48 hours, the resulting multilayer MXene was centrifuged, washed repeatedly with deionized water, and freeze-dried for 20-24 hours. Then, it was stirred again at 40-50℃ for 12-14 hours. Then, the treated MXene was centrifuged at 8000-9000 r / min to obtain a precipitate. Subsequently, the obtained black powder was dispersed in 80-100 mL of water and sonicated under argon atmosphere for 2-2.5 hours. Finally, the mixed solution was centrifuged at 3500-4000 r / min, the filtrate was collected, and it was freeze-dried to obtain multilayer MXene. Two parts of the prepared MXene were added to 20 parts of the prepared PAA solution and stirred for 2-2.5 hours. Then, the PAA / MXene solution was mixed evenly with the positive electrode active material and further thermal imidization was carried out in a high-temperature oven to obtain a branched porous PI / MXene-coated positive electrode active material.

[0050] (3) Preparation of a branched porous PI / MXene / polypyrrole composite coating positive electrode active material with a dual conductivity mechanism and assembly of a lithium-ion battery: The positive electrode active material with a porous PI / MXene coating obtained above was subjected to in-situ polymerization to cover a polypyrrole layer, as follows: 1 wt% of pyrrole monomer and the original positive electrode active material with a branched porous PI / MXene coating were added to anhydrous ethanol and stirred thoroughly for 2-3 h. Then, it was added to the above mixture at a molar ratio (pyrrole monomer: sodium p-toluenesulfonate = 3:1), wherein sodium p-toluenesulfonate was added to the above mixture as a dopant. Next, FeCl3·6H2O was dissolved in anhydrous ethanol and added to the solution at a molar ratio (pyrrole monomer: FeCl3·6H2O = 1:1). Then, the mixture was stirred thoroughly in an ice-water bath. After complete reaction, the mixture was filtered and washed. The cathode material with a branched porous PI / MXene / polypyrrole composite coating layer and a dual conductivity mechanism was obtained by drying under vacuum at 50-60℃ for 10-12 hours. The coated cathode material, conductive carbon black, and PVDF were weighed at a mass ratio of 8:1:1, mixed, and NMP solvent was added to adjust the viscosity. The mixture was then stirred at a constant temperature and speed using a magnetic stirrer for 5-6 hours to ensure homogeneity. 2-3 ml of the cathode slurry was then dropped onto carbon-containing aluminum foil using a dropper, and uniformly coated using a 100 μm scraper. The mixture was then placed in a constant temperature oven at 60-70℃ for 3-4 hours to remove the solvent. The dried current collector was cut into 12 μm circular electrodes using an electrode punching machine, and then rolled using a roller press. The above steps successfully produced a positive electrode coated with polyimide. The lithium-ion button cell was assembled in an argon-filled glove box. The selected separator was a Celgard-2400, cut into 25μm discs using a cutting machine for later use. The electrolyte contained 1 mol / L... -1 A solution of DMC / EC / EMC (volume ratio 1:1:1) was prepared, and lithium sheet was used as the negative electrode.

[0051] Following the electrode preparation and battery assembly and testing methods described above, the lithium-ion battery assembled using this system exhibits a 0.1C discharge specific capacity of 197 mAh / g, an initial efficiency of 86.34%, and a capacity retention rate of 89.1% after 100 cycles at 0.1C.

[0052] Example 5

[0053] Unlike Example 1, this embodiment changes the proportion of polyimide in the preparation of the composite-coated positive electrode active material. The other steps are the same as in Example 1. The specific implementation steps are as follows:

[0054] (1) Preparation of polyamic acid precursor for polyimide coating: The solid content of the PAA solution was set to 15%. N-methylpyrrolidone (NMP) was used as the solvent. The polyamic acid precursor solution for polyimide was prepared using a synthesis system of 1,4,5,8-naphthalenetetracarboxylic anhydride (NTCDA), p-phenylenediamine (p-PDA), and 1,3,5-tris(4-aminophenyl)benzene (TAPB). The molar ratio of total anhydride groups to total amino groups was 1.01:1, and the molar amount of triamine TAPB accounted for 2% of the total molar amount of monomers. 3.894 g of NTCDA, 1.570 g of p-PDA, and 0.200 g of TAPB were weighed and set aside. 20 ml of NMP solution was added to a three-necked flask, followed by 1.570 g of p-PDA and 0.200 g of TAPB. The solid reagents were allowed to dissolve. Turn on the electric stirrer and wait for p-PDA and TAPB to completely dissolve in NMP solvent under mechanical stirring, then connect to an ice-water bath. Next, add NTCDA in batches, completing the addition after approximately 1 hour. After the addition is complete, rinse the volumetric flask with the remaining 10 ml of NMP solution and slowly add the solution along the wall of the three-necked flask. Continue stirring until the solution viscosity increases. Once the "climbing rod effect" is observed, continue stirring for approximately 3 hours to prepare the polyamic acid precursor solution for polyimide.

[0055] (2) Preparation of branched porous PI / MXene-coated positive electrode active material: 3-5 parts of LiF and 3-5 parts of hydrochloric acid solution were mixed in a beaker at 40-50℃. Then, 1-2 parts of Ti3AlC2 powder were slowly added to the solution to avoid releasing a large amount of heat. After stirring for 40-48 hours, the resulting multilayer MXene was centrifuged, washed repeatedly with deionized water, and freeze-dried for 20-24 hours. Then, it was stirred again at 40-50℃ for 12-14 hours. Then, the treated MXene was centrifuged at 8000-9000 r / min to obtain a precipitate. Subsequently, the obtained black powder was dispersed in 80-100 mL of water and sonicated under argon atmosphere for 2-2.5 hours. Finally, the mixed solution was centrifuged at 3500-4000 r / min, the filtrate was collected, and it was freeze-dried to obtain multilayer MXene. Two parts of the prepared MXene were added to 50 parts of the prepared PAA solution and stirred for 2-2.5 hours. Then, the PAA / MXene solution was mixed evenly with the positive electrode active material and further thermal imidization was carried out in a high-temperature oven to obtain a branched porous PI / MXene-coated positive electrode active material.

[0056] (3) Preparation of a branched porous PI / MXene / polypyrrole composite coating positive electrode active material with a dual conductivity mechanism and assembly of a lithium-ion battery: The positive electrode active material with a porous PI / MXene coating obtained above was subjected to in-situ polymerization to cover a polypyrrole layer, as follows: 0.5 wt% of pyrrole monomer and the original positive electrode active material with a branched porous PI / MXene coating were added to anhydrous ethanol and stirred thoroughly for 2-3 h. Then, it was added to the above mixture at a molar ratio (pyrrole monomer: sodium p-toluenesulfonate = 3:1), wherein sodium p-toluenesulfonate was added to the above mixture as a dopant. Next, FeCl3·6H2O was dissolved in anhydrous ethanol and added to the solution at a molar ratio (pyrrole monomer: FeCl3·6H2O = 1:1). Then, the mixture was stirred thoroughly in an ice-water bath. After complete reaction, the mixture was filtered and washed. The cathode material with a branched porous PI / MXene / polypyrrole composite coating layer and a dual conductivity mechanism was obtained by drying under vacuum at 50-60℃ for 10-12 hours. The coated cathode material, conductive carbon black, and PVDF were weighed at a mass ratio of 8:1:1, mixed, and NMP solvent was added to adjust the viscosity. The mixture was then stirred at a constant temperature and speed using a magnetic stirrer for 5-6 hours to ensure homogeneity. 2-3 ml of the cathode slurry was then dropped onto carbon-containing aluminum foil using a dropper, and uniformly coated using a 100 μm scraper. The mixture was then placed in a constant temperature oven at 60-70℃ for 3-4 hours to remove the solvent. The dried current collector was cut into 12 μm circular electrodes using an electrode punching machine, and then rolled using a roller press. The above steps successfully produced a positive electrode coated with polyimide. The lithium-ion button cell was assembled in an argon-filled glove box. The selected separator was a Celgard-2400, cut into 25μm discs using a cutting machine for later use. The electrolyte contained 1 mol / L... -1 A solution of DMC / EC / EMC (volume ratio 1:1:1) was prepared, and lithium sheet was used as the negative electrode.

[0057] Following the electrode preparation and battery assembly and testing methods described above, the lithium-ion battery assembled using this system exhibits a 0.1C discharge specific capacity of 198.64 mAh / g, an initial efficiency of 86.65%, and a capacity retention of 89.25% after 100 cycles at 0.1C.

[0058] Example 6

[0059] Unlike Example 1, this embodiment modifies the chemical structure of the polyimide in preparing the composite-coated positive electrode active material, replacing 1,4,5,8-naphthalenetetracarboxylic anhydride (NTCDA) with a monomer containing an ether oxygen bond, 4,4'-biphenyl ether dianhydride (ODPA). The other steps are the same as in Example 1. The specific implementation steps are as follows:

[0060] (1) Preparation of polyamic acid precursor for polyimide coating: The solid content of the PAA solution was set to 15%. N-methylpyrrolidone (NMP) was used as the solvent. The polyamic acid precursor solution for polyimide was prepared using a synthesis system of 4,4'-diphenyl ether dianhydride (ODPA), p-phenylenediamine (p-PDA), and 1,3,5-tris(4-aminophenyl)benzene (TAPB). The molar ratio of total anhydride groups to total amino groups was 1.01:1, and the molar amount of triamine TAPB accounted for 2% of the total molar amount of monomers. 4.051 g of ODPA, 1.412 g of p-PDA, and 0.183 g of TAPB were weighed and set aside. 20 ml of NMP solution was added to a three-necked flask, followed by 1.412 g of p-PDA and 0.183 g of TAPB. The solid reagents were allowed to dissolve. Turn on the electric stirrer and wait for p-PDA and TAPB to completely dissolve in NMP solvent under mechanical stirring, then connect to an ice-water bath. Next, add ODPA in batches, completing the addition in about 1 hour. After the addition is complete, rinse the volumetric flask with the remaining 10 ml of NMP solution and slowly add the solution along the wall of the three-necked flask. Continue stirring until the solution viscosity increases. Once the "climbing rod effect" is observed, continue stirring for about 3 hours to prepare the polyamic acid precursor solution for polyimide.

[0061] (2) Preparation of branched porous PI / MXene-coated positive electrode active material: 3-5 parts of LiF and 3-5 parts of hydrochloric acid solution were mixed in a beaker at 40-50℃. Then, 1-2 parts of Ti3AlC2 powder were slowly added to the solution to avoid releasing a large amount of heat. After stirring for 40-48 hours, the resulting multilayer MXene was centrifuged, washed repeatedly with deionized water, and freeze-dried for 20-24 hours. Then, it was stirred again at 40-50℃ for 12-14 hours. Then, the treated MXene was centrifuged at 8000-9000 r / min to obtain a precipitate. Subsequently, the obtained black powder was dispersed in 80-100 mL of water and sonicated under argon atmosphere for 2-2.5 hours. Finally, the mixed solution was centrifuged at 3500-4000 r / min, the filtrate was collected, and it was freeze-dried to obtain multilayer MXene. Two parts of the prepared MXene were added to 20 parts of the prepared PAA solution and stirred for 2-2.5 hours. Then, the PAA / MXene solution was mixed evenly with the positive electrode active material and further thermal imidization was carried out in a high-temperature oven to obtain a branched porous PI / MXene-coated positive electrode active material.

[0062] (3) The above-obtained positive electrode active material with a porous PI / MXene coating was subjected to in-situ polymerization to cover a polypyrrole layer. The method was as follows: 0.5 wt% of pyrrole monomer and the original positive electrode active material with a branched porous PI / MXene coating were added to anhydrous ethanol and stirred thoroughly for 2-3 h. Then, it was added to the mixture at a molar ratio (pyrrole monomer: sodium p-toluenesulfonate = 3:1), where sodium p-toluenesulfonate was added as a dopant. Next, FeCl3·6H2O was dissolved in anhydrous ethanol and added to the solution at a molar ratio (pyrrole monomer: FeCl3·6H2O = 1:1). The mixture was then thoroughly stirred in an ice-water bath. After complete reaction, the mixture was filtered and washed. It was dried under vacuum at 50-60°C for 10-12 h to obtain a positive electrode material with a branched porous PI / MXene / polypyrrole composite coating exhibiting a dual conductivity mechanism. Weigh the coated positive electrode material, conductive carbon black, and PVDF according to a mass ratio of 8:1:1, mix them, and add NMP solvent to adjust the viscosity. Then, use a magnetic stirrer to stir at a constant temperature and speed for 5-6 hours to ensure the system is homogeneous. Next, use a dropper to take 2-3 ml of the positive electrode slurry and drop it onto carbon-containing aluminum foil. Use a 100 μm scraper to coat it evenly, and then place it in a constant temperature oven at 60-70℃ for 3-4 hours to remove the solvent. Use an electrode sheet punching machine to cut the dried current collector into 12 μm circular electrode sheets, and then use a roller press to roll the electrode sheets. The above steps successfully produce a positive electrode sheet coated with polyimide. The lithium-ion coin cell half-cell was assembled in an argon-filled glove box. The selected separator model was Celgard-2400, which was cut into 25 μm circular sheets using a cutting machine for subsequent use. The electrolyte contained 1 mol / L... -1 A solution of DMC / EC / EMC (volume ratio 1:1:1) was prepared, and lithium sheet was used as the negative electrode.

[0063] Following the electrode preparation and battery assembly and testing methods described above, the lithium-ion battery assembled using this system exhibits a 0.1C discharge specific capacity of 199.45 mAh / g, an initial efficiency of 87.8%, and a capacity retention rate of 90.3% after 100 cycles at 0.1C.

[0064] Example 7

[0065] Unlike Example 1, in this embodiment, the dopant used in the synthesis of polypyrrole is changed from sodium p-benzenesulfonate to hexadecyltrimethylammonium bromide when preparing the composite-coated positive electrode active material. The other steps are the same as in Example 1. The specific implementation steps are as follows:

[0066] (1) Preparation of polyamic acid precursor for polyimide coating: The solid content of the PAA solution was set to 15%. N-methylpyrrolidone (NMP) was used as the solvent. The polyamic acid precursor solution for polyimide was prepared using a synthesis system of 1,4,5,8-naphthalenetetracarboxylic anhydride (NTCDA), p-phenylenediamine (p-PDA), and 1,3,5-tris(4-aminophenyl)benzene (TAPB). The molar ratio of total anhydride groups to total amino groups was 1.01:1, and the molar amount of triamine TAPB accounted for 2% of the total molar amount of monomers. 3.894 g of NTCDA, 1.570 g of p-PDA, and 0.200 g of TAPB were weighed and set aside. 20 ml of NMP solution was added to a three-necked flask, followed by 1.570 g of p-PDA and 0.200 g of TAPB. The solid reagents were allowed to dissolve. Turn on the electric stirrer and wait for p-PDA and TAPB to completely dissolve in NMP solvent under mechanical stirring, then connect to an ice-water bath. Next, add NTCDA in batches, completing the addition after approximately 1 hour. After the addition is complete, rinse the volumetric flask with the remaining 10 ml of NMP solution and slowly add the solution along the wall of the three-necked flask. Continue stirring until the solution viscosity increases. Once the "climbing rod effect" is observed, continue stirring for approximately 3 hours to prepare the polyamic acid precursor solution for polyimide.

[0067] (2) Preparation of branched porous PI / MXene-coated positive electrode active material: 3-5 parts of LiF and 3-5 parts of hydrochloric acid solution were mixed in a beaker at 40-50℃. Then, 1-2 parts of Ti3AlC2 powder were slowly added to the solution to avoid releasing a large amount of heat. After stirring for 40-48 hours, the resulting multilayer MXene was centrifuged, washed repeatedly with deionized water, and freeze-dried for 20-24 hours. Then, it was stirred again at 40-50℃ for 12-14 hours. Then, the treated MXene was centrifuged at 8000-9000 r / min to obtain a precipitate. Subsequently, the obtained black powder was dispersed in 80-100 mL of water and sonicated under argon atmosphere for 2-2.5 hours. Finally, the mixed solution was centrifuged at 3500-4000 r / min, the filtrate was collected, and it was freeze-dried to obtain multilayer MXene. Two parts of the prepared MXene were added to 20 parts of the prepared PAA solution and stirred for 2-2.5 hours. Then, the PAA / MXene solution was mixed evenly with the positive electrode active material and further thermal imidization was carried out in a high-temperature oven to obtain a branched porous PI / MXene-coated positive electrode active material.

[0068] (3) Preparation of a branched porous PI / MXene / polypyrrole composite coating positive electrode active material with a dual conductivity mechanism and assembly of a lithium-ion battery: The positive electrode active material with a porous PI / MXene coating obtained above was subjected to in-situ polymerization to cover a polypyrrole layer, as follows: 0.5 wt% of pyrrole monomer and the original positive electrode active material with a branched porous PI / MXene coating were added to anhydrous ethanol and stirred thoroughly for 2-3 h. Then, it was added to the above mixture at a molar ratio (pyrrole monomer: hexadecyltrimethylammonium bromide = 3:1), wherein hexadecyltrimethylammonium bromide was added to the above mixture as a dopant. Next, FeCl3·6H2O was dissolved in anhydrous ethanol and added to the solution at a molar ratio (pyrrole monomer: FeCl3·6H2O = 1:1). Then, the mixture was stirred thoroughly in an ice-water bath. After complete reaction, the mixture was filtered and washed. The cathode material with a branched porous PI / MXene / polypyrrole composite coating layer and a dual conductivity mechanism was obtained by drying under vacuum at 50-60℃ for 10-12 hours. The coated cathode material, conductive carbon black, and PVDF were weighed at a mass ratio of 8:1:1, mixed, and NMP solvent was added to adjust the viscosity. The mixture was then stirred at a constant temperature and speed using a magnetic stirrer for 5-6 hours to ensure homogeneity. 2-3 ml of the cathode slurry was then dropped onto carbon-containing aluminum foil using a dropper, and uniformly coated using a 100 μm scraper. The mixture was then placed in a constant temperature oven at 60-70℃ for 3-4 hours to remove the solvent. The dried current collector was cut into 12 μm circular electrodes using an electrode punching machine, and then rolled using a roller press. The above steps successfully produced a positive electrode coated with polyimide. The lithium-ion button half-cell was assembled in an argon-filled glove box. The selected separator was a Celgard-2400, cut into 25μm discs using a cutting machine for later use. The electrolyte contained 1 mol / L... -1 A solution of DMC / EC / EMC (volume ratio 1:1:1) was used, with lithium foil as the negative electrode. Following the electrode preparation and the aforementioned method, the battery was assembled and tested. The assembled lithium-ion battery exhibited a 0.1C discharge specific capacity of 196.53 mAh / g, an initial efficiency of 85.4%, and a capacity retention of 87.98% after 100 cycles at 0.1C.

[0069] Comparative Example 1

[0070] First, a PVDF solution with a solid content of 8% was prepared. 5g of white powdered PVDF binder was weighed and added to NMP solution until 62.5g was reached. The mixture was stirred until homogeneous to obtain the desired PVDF solution. NCM811, conductive carbon black, and PVDF were mixed in NMP solvent at a mass ratio of 8:1:1. A positive electrode slurry was prepared by mechanical stirring, and NMP solvent was added to adjust the viscosity to a solid-liquid ratio of 4:6. The positive electrode slurry was uniformly coated onto the current collector and then dried in a vacuum oven at 70℃ for 4 hours. After cutting and rolling, a positive electrode sheet with PVDF as the binder was obtained. The lithium-ion coin cell was assembled in an argon-filled glove box. The separator used was Celgard-2400, which was cut into 25μm discs using a cutting machine for later use. The electrolyte contained 1 mol / L... -1 A solution of DMC / EC / EMC (volume ratio 1:1:1) was prepared, and lithium sheet was used as the negative electrode.

[0071] Following the electrode preparation and battery assembly and testing methods described above, the lithium-ion battery assembled using this system exhibits a 0.1C discharge specific capacity of 189.21 mAh / g, an initial efficiency of 84.3%, and a capacity retention rate of 81.2% after 100 cycles at 0.1C.

[0072] Comparative Example 2

[0073] First, a PVDF solution with a solid content of 8% was prepared. 5g of white powdered PVDF binder was weighed and added to NMP solution until 62.5g was reached. The mixture was stirred until homogeneous to obtain the desired PVDF solution. NCM811, conductive carbon black, and PVDF were mixed in NMP solvent at a mass ratio of 92:5:3. A positive electrode slurry was prepared by mechanical stirring, and NMP solvent was added to adjust the viscosity to a solid-liquid ratio of 4:6. The positive electrode slurry was uniformly coated onto the current collector and then dried in a vacuum oven at 70℃ for 4 hours. After cutting and rolling, a positive electrode sheet with PVDF as the binder was obtained. The lithium-ion coin cell was assembled in an argon-filled glove box. The separator used was Celgard-2400, which was cut into 25μm discs using a cutting machine for later use. The electrolyte contained 1 mol / L... -1 A solution of DMC / EC / EMC (volume ratio 1:1:1) was prepared, and lithium sheet was used as the negative electrode.

[0074] The battery was assembled and tested according to the above electrode preparation and the aforementioned method. The lithium-ion battery assembled by this system has a 0.1C discharge specific capacity of 188mAh / g, an initial efficiency of 83.6%, and a capacity retention rate of 82.4% after 100 cycles at 0.1C.

[0075] Comparative Example 3

[0076] Take 5g of NCM811 cathode material powder into a beaker containing anhydrous ethanol, and stir vigorously in a water bath until homogeneous. Separately, dissolve a 0.5wt% Co3O4 solution in Co(NO3)2·6(H2O). Stir both solutions in a water bath until the solvent evaporates, and then dry the resulting product in an oven. Calcine the dried sample at 500℃ for 5 hours in air. The resulting sample is the Co3O4-coated cathode material. Mix the Co3O4-coated cathode material, conductive carbon black, and a prepared 8% solid-content PVDF solution in NMP solvent at a ratio of 8:1:1. Prepare a cathode slurry by mechanical stirring, and adjust the viscosity with NMP solvent to a solid-liquid ratio of 4:6. Coat the cathode slurry uniformly onto a current collector, and then dry it in a vacuum oven at 70℃ for 4 hours. After cutting and rolling, obtain the Co3O4-coated cathode sheet. The lithium-ion button half-cell was assembled in an argon-filled glove box. The selected separator was a Celgard-2400, cut into 25μm discs using a cutting machine for later use. The electrolyte contained 1 mol / L... -1 A solution of DMC / EC / EMC (volume ratio 1:1:1) was prepared, and lithium sheet was used as the negative electrode.

[0077] Following the electrode preparation and battery assembly and testing methods described above, the lithium-ion battery assembled using this system exhibits a 0.1C discharge specific capacity of 190.38 mAh / g, an initial efficiency of 84.2%, and a capacity retention rate of 83.5% after 100 cycles at 0.1C.

[0078] Comparative Example 4

[0079] TiF4 was dissolved in anhydrous ethanol to prepare a 10% (w / w) homogeneous solution. Then, NCM811 powder was added to the solution at a mass ratio of TiF4:NCM811 = 1%. After sonication for 20 min, the solution was vacuum dried for 5 h and then heated in a tube furnace for 5 h to obtain the TiO2-coated cathode material. The TiO2-coated cathode material, conductive carbon black, and a prepared 8% solid-content PVDF solution were mixed in NMP solvent at a mass ratio of 8:1:1. A cathode slurry was prepared by mechanical stirring, and NMP solvent was added to adjust the viscosity to a solid-liquid ratio of 4:6. The cathode slurry was uniformly coated onto a current collector and then dried in a vacuum oven at 70°C for 4 h. After cutting and rolling, the TiO2-coated cathode sheet was obtained. The lithium-ion button half-cell was assembled in an argon-filled glove box. The selected separator was a Celgard-2400, cut into 25μm discs using a cutting machine for later use. The electrolyte contained 1 mol / L... -1A solution of DMC / EC / EMC (volume ratio 1:1:1) was prepared, and lithium sheet was used as the negative electrode.

[0080] Following the electrode preparation and battery assembly and testing methods described above, the lithium-ion battery assembled using this system exhibits a 0.1C discharge specific capacity of 192.49 mAh / g, an initial efficiency of 85.7%, and a capacity retention rate of 83% after 100 cycles at 0.1C.

[0081] Table 1. Performance of the positive electrode sheets prepared in the examples and comparative examples

[0082]

[0083] As shown in Table 1, lithium-ion batteries assembled using a branched porous polyimide / MXene / polypyrrole composite coating with a dual-conductivity mechanism generally exhibit higher discharge specific capacity at 0.1C, higher initial coulombic efficiency, and higher capacity retention after 100 cycles compared to batteries using uncoated cathode active materials, as well as those coated with Co3O4 and TiO2. This indicates that the composite coating plays a crucial role in maintaining cathode structural stability, effectively promoting cathode capacity utilization, and improving long-cycle stability. Furthermore, compared to traditional inorganic coatings like Co3O4 and TiO2, the advantages of the composite coating are more significant. Figure 4 and Figure 5 It can be seen that after 100 cycles, the surface of the uncoated positive electrode active material developed large cracks, while the structure of the coated positive electrode material remained relatively intact. This proves that the presence of the branched porous polyimide / MXene / polypyrrole composite coating layer with dual conductivity mechanism does indeed play a role in maintaining the structural stability of the positive electrode active material during battery cycling.

[0084] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery cathode material with a branched porous polyimide / MXene / polypyrrole composite coating having a dual conductivity mechanism and its preparation method, characterized in that, The composite coating layer is applied to the surface of the positive electrode active particles by wet chemical deposition and in-situ polymerization, with a thickness of 2-5 nm. The positive electrode material modified by the composite coating is used to prepare electrode sheets for use in lithium batteries, which can significantly improve the cycle stability and service life of the battery.

2. The positive electrode material with a branched porous polyimide / MXene / polypyrrole composite coating having a dual conductivity mechanism and its preparation method according to claim 1, characterized in that, Includes the following steps; A: Polyamic acid solution is synthesized by solution polycondensation. Polyamine is dissolved in an organic solvent, and polyacid anhydride is added in batches. The precursor solution (polyamic acid solution) is obtained by mechanical stirring in an ice-water bath. B: In a beaker, LiF is mixed with hydrochloric acid solution at a certain temperature. Then, Ti3AlC2 powder is slowly added to the solution to avoid releasing a large amount of heat. After stirring for a period of time, the resulting multilayer MXene is centrifuged, washed repeatedly with deionized water, and freeze-dried. Then, stirring is continued for a period of time. The treated multilayer MXene is then centrifuged to obtain a precipitate. Subsequently, the obtained black powder is dispersed in water and sonicated under argon atmosphere. Finally, the mixed solution is centrifuged at a certain speed, the filtrate is collected, and it is freeze-dried to obtain a few-layer MXene. C: Add the MXene obtained in B to the PAA solution prepared in A, stir evenly to obtain a PAA / MXene solution, then mix the PAA / MXene solution with the positive electrode active material evenly, and perform further thermal imidization treatment in a high-temperature oven to obtain a branched porous PI / MXene-coated positive electrode active material. The coating method used is wet chemical deposition, and the coating thickness is 1-3 nm. D: The branched porous PI / MXene-coated positive electrode active material obtained in C is subjected to in-situ polymerization to cover a polypyrrole layer. The method is as follows: Pyrrole monomer and the original positive electrode active material with branched porous PI / MXene coating are added to anhydrous ethanol and stirred thoroughly. Then, the monomer and sodium p-toluenesulfonate are added to the above mixture. Next, FeCl3·6H2O is dissolved in anhydrous ethanol and added to the solution. Then, the mixture is stirred thoroughly in an ice-water bath. After the reaction is complete, the mixture is filtered and washed, and dried under vacuum to obtain a positive electrode active material with a branched porous PI / MXene / conductive polymer composite coating.

3. The positive electrode material with a branched porous polyimide / MXene / polypyrrole composite coating having a dual conductivity mechanism and its preparation method according to claim 2, characterized in that, The polyimide mentioned in step A is any polydicarboxylic acid anhydride and polyamine prepared by solution condensation polymerization. The polydicarboxylic acid anhydride is selected from 4,4'-(hexafluoroisopropene) phthalic anhydride (6FDA), pyromellitic dianhydride (PMDA), biphenyl dianhydride (BPDA), 4,4'-diphenyl ether dianhydride (ODPA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenyl sulfone tetracarboxylic dianhydride (DSDA), 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA), 1,4,5,8 1,4'-naphthalenetetracarboxylic anhydride (NTCDA); wherein the polyamine is selected from one or more of 4,4'-diaminodiphenyl sulfone (DDS), 4,4'-diaminodiphenyl ether (ODA), aminopropyl-terminated polydimethylsiloxane (DMS), 3,5'-diaminobenzoic acid (DABA), m-phenylenediamine (mPDA), p-phenylenediamine (p-PDA), 1,3,5-tris(4-aminophenyl)benzene (TAPB), 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), and 3,6-diaminocarbazole (DAC).

4. The positive electrode material with a branched porous polyimide / MXene / polypyrrole composite coating having a dual conductivity mechanism and its preparation method according to claim 2, characterized in that, The solvent mentioned in step A is one or a combination of two or more of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc).

5. The positive electrode material with a branched porous polyimide / MXene / polypyrrole composite coating having a dual conductivity mechanism and its preparation method according to claim 2, characterized in that, In step B, take 3-5 parts of LiF and 3-5 parts of hydrochloric acid, mix them at 40-50℃, take 1-2 parts of Ti3AlC2 powder, stir for 40-48 hours, freeze dry for 20-24 hours, continue stirring at 40-50℃ for 12-14 hours, start centrifugation speed at 8000-9000 r / min, disperse in 80-100 ml of water, sonicate for 2-2.5 hours, and finally centrifuge at 3500-4000 r / min.

6. The positive electrode material with a branched porous polyimide / MXene / polypyrrole composite coating having a dual conductivity mechanism and its preparation method according to claim 2, characterized in that, Take 2-3 parts of the MXene obtained in step C, add it to 20-50 parts of PAA solution, and stir for 2-2.5 hours. The positive electrode active material includes one or more of the following materials: lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based positive electrode material, lithium manganese oxide, high-voltage spinel lithium nickel manganese oxide, lithium manganese phosphate, lithium cobalt phosphate, lithium nickel phosphate, lithium lithium rich layered oxide, etc. The coating method is wet chemical deposition, the coating thickness is 1-3 nm, the solid content of polyamic acid solution is 10%-20%, and the high-temperature thermal imidization procedure is as follows: first heat to the pre-imidization temperature of 135-140℃ at 2-2.5℃ / min, hold for 30-40 min, and then continue to heat to 295-300℃ at 2-2.5℃ / min, and hold for 60-70 min.

7. The positive electrode material with a branched porous polyimide / MXene / polypyrrole composite coating having a dual conductivity mechanism and its preparation method according to claim 2, characterized in that, In step D, the pyrrole monomer used is 0.5-1 wt%, the molar ratio of monomer to sodium p-toluenesulfonate is 3:1, wherein sodium p-toluenesulfonate is added to the above mixture as a dopant, the molar ratio of monomer to FeCl3·6H2O is 1:1, the coating method is in-situ polymerization, the coating thickness is 1-3 nm, the subsequent stirring time is 2-3 h, the vacuum drying temperature is 50-60 °C, and the drying time is 10-12 h.

8. A branched porous polyimide / MXene / polypyrrole composite coated and modified cathode material with a dual conductivity mechanism, prepared by the preparation method of any one of claims 1-7.

9. A lithium battery, characterized in that, The positive electrode of the battery contains a branched porous polyimide / MXene / polypyrrole composite coating layer with a dual conductivity mechanism, which is prepared by wet chemical deposition and in-situ polymerization.

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