CN118970359A

CN118970359A - A polyetherimide diaphragm chemically modified with fatty diamine, a preparation method thereof, and application thereof in lithium/magnesium batteries

Info

Publication number: CN118970359A
Application number: CN202411004966.2A
Authority: CN
Inventors: 郑金云; 孙亚娜; 冯祥明; 陈卫华
Original assignee: Zhengzhou University
Current assignee: Zhengzhou University
Priority date: 2024-07-25
Filing date: 2024-07-25
Publication date: 2024-11-15

Abstract

The invention provides a fatty diamine chemically modified polyetherimide membrane, a preparation method thereof and application thereof in a lithium/magnesium battery. Dissolving polyetherimide and a pore-forming agent in an organic solvent to form a casting solution, solidifying the casting solution into a film by a phase inversion method, and then drying to obtain a polyetherimide film; immersing the polyetherimide membrane into a fatty diamine solution, and then drying to obtain the fatty diamine chemically modified polyetherimide membrane. The obtained aliphatic diamine chemically modified polyetherimide diaphragm is rich in polar groups, has moderate and uniform pore diameter, large porosity, smaller contact angle and stronger ion transmission capacity, effectively improves the thermal stability of the diaphragm and the interface performance of a battery, can be assembled with various electrode materials, and has better cycle stability than commercial polyolefin diaphragms for assembled lithium ion batteries and magnesium ion batteries.

Description

Aliphatic diamine chemically modified polyetherimide diaphragm, preparation method thereof and application thereof in lithium/magnesium battery

Technical Field

The invention belongs to the field of lithium/magnesium ion battery diaphragms, and particularly relates to a fatty diamine chemically modified polyetherimide diaphragm, a preparation method thereof and application thereof in lithium/magnesium batteries.

Background

The battery is used as a new generation green high specific energy device, plays an important role in the field of new energy storage, and is widely applied to the fields of electronic products, electric automobiles and the like. The composition of the battery comprises a positive electrode, a negative electrode, a separator, an electrolyte and the like. The separator is important to the composition and safety of the lithium/magnesium ion battery, and on one hand, the separator separates the anode from the cathode to prevent the direct contact of the anode and the cathode from short circuit to cause safety accidents. On the other hand, the porous structure inside the separator allows the metal ions in the electrolyte to migrate freely between the electrodes. At present, the commercialized diaphragm is mainly based on polyolefin materials, and the diaphragm has the defects of low melting point, poor thermal stability, limited matching electrolyte caused by poor wettability to the electrolyte and the like although the diaphragm has better mechanical property and electrochemical stability. Therefore, it is important to develop a novel battery separator that is nonflammable and electrolyte-philic and that can be used under high temperature conditions.

Polyetherimide (PEI) is used as engineering plastic and has high strength, rigidity, wear resistance and dimensional stability. At the same time, it has a broad range of chemical resistance, including resistance to most hydrocarbons, alcohols, inorganic acids and all halogenated solvents. Meanwhile, the polyetherimide contains a plurality of polar groups, so that the polyetherimide has better electrolyte wettability. Patent CN109860483a discloses a polyetherimide coating liquid, a coating base film, a manufacturing method thereof and application in secondary batteries. The method can keep the original stability of the polyetherimide solution to the maximum extent, and the diaphragm coating liquid has good heat shrinkage performance by adding inorganic particles. But the coating method tends to block the pores of the base film and is disadvantageous in terms of ion transport, thereby affecting battery performance. The patent CN106876630 a provides a crosslinked polyetherimide porous membrane and is applied to lithium ion batteries, and shows better mechanical properties and thermal stability. The patent utilizes a humidity phase inversion method to obtain a polyetherimide diaphragm, then uses p-xylylenediamine as a cross-linking agent, and obtains the cross-linked polyetherimide porous diaphragm by adjusting the cross-linking time, wherein the porosity of the diaphragm is about 50-75%, the contact angle is 39-50 ℃, and the assembled lithium ion battery can run for 55-200 cycles. The modified polyetherimide disclosed in the patent has the problems of low void ratio, poor wettability with electrolyte, incapability of long-term stable circulation and the like.

Disclosure of Invention

Aiming at the technical problems in the prior art, the invention provides a fatty diamine chemically modified polyetherimide membrane, a preparation method thereof and application thereof in lithium/magnesium batteries. The porous PEI membrane obtained by the invention has larger and coherent pores, and then the PEI membrane is structurally modified by using aliphatic diamine with smaller molecular weight and incompletely forms a cross-linked structure, so that the wettability and ion transmission capacity of the membrane are effectively improved, and the cycle stability and safety of a lithium/magnesium battery are improved.

In order to achieve the above purpose, the technical scheme of the invention is realized as follows:

A method for preparing a polyether imide diaphragm chemically modified by aliphatic diamine, which comprises the following steps:

(1) Dissolving polyetherimide and a pore-forming agent in an organic solvent I to form a casting solution, solidifying the casting solution into a film by a phase inversion method, and then drying to obtain a polyetherimide film;

(2) Immersing the polyetherimide film in the step (1) into a fatty diamine solution, and then drying to obtain the fatty diamine chemically modified polyetherimide diaphragm.

The obtained modified diaphragm has an amino group with an exposed tail end, and the polar group is beneficial to improving the wettability and ion transmission capacity of the diaphragm, improving the interface performance of the battery and improving the cycle stability and the multiplying power performance of the battery. And the modified diaphragm effectively improves the combustion performance and the safety performance of the diaphragm.

The pore-forming agent in the step (1) is polyvinylpyrrolidone or polyethylene glycol, and the molecular weight of the pore-forming agent is 100-150 ten thousand; the organic solvent I is N, N-dimethylacetamide, N-dimethylformamide or N-methylpyrrolidone.

The concentration of the polyetherimide in the step (1) in the film casting solution is 14-18wt%, preferably 15-16wt%; the concentration of the pore-forming agent in the casting solution is 3-13wt%; preferably, the concentration is 8-12wt%; at the moment, the pores of the membrane are communicated most uniformly, the contact angle of the prepared PEI membrane is minimum, and the porosity is maximum; the molecular weight and concentration of the pore former affect the porosity.

The phase inversion method in the step (1) is to knife-coat the casting solution into a film, then put the film in saturated water vapor for 10-15s, then immerse the film in deionized water for solidification and remove the pore-forming agent.

The concentration of the aliphatic diamine in the solution in the step (2) is 4-8wt%; the polyether imide is soaked in the aliphatic diamine solution for 6-10h; the solvent of the aliphatic diamine solution is methanol, ethanol or N-methyl pyrrolidone; the aliphatic diamine in the step is ethylenediamine, propylenediamine, butylenediamine, pentylene diamine or hexamethylenediamine.

The aliphatic diamine chemically modified polyetherimide has structural units represented by the general formula (I):

General formula (I)

Where m= 1,1.5,2,2.5 or 3.

The thickness of the aliphatic diamine chemically modified polyetherimide membrane is 30-60 mu m, and preferably the membrane thickness is 40-45 mu m.

The application of the aliphatic diamine chemical modified polyetherimide diaphragm in a battery is that the battery is a lithium ion battery or a magnesium ion battery.

The lithium ion battery comprises a positive electrode material, a negative electrode material, electrolyte and a battery diaphragm; the lithium ion battery anode material comprises an anionic, layered oxide or organic electrode material; the anions are polyanions such as lithium iron phosphate, lithium manganese phosphate and the like; the layered oxide is lithium cobaltate or lithium manganate; the organic electrode material is ternary material or Prussian blue; the negative electrode material is selected from any one of metal lithium, alloy compound, metal oxide, metal sulfide, metal phosphide, carbon material, lamellar compound or organic matter; the alloy compound is two or more of tin, aluminum, bismuth, antimony or zinc metal compounds, and the metal oxide is TiO ₂; the metal sulfide is FeS, snS, snS ₂ or FeS ₂; the metal phosphide is Sn ₃P₄; the carbon material is hard carbon or soft carbon; the lamellar compound is graphite, MXene, moS ₂ or black phosphorus; the organic matter is polyimide or polyphenyl quinone.

The magnesium ion battery comprises a positive electrode material, a negative electrode material, electrolyte and a battery diaphragm; the positive electrode material of the magnesium ion battery comprises CuFeSe ₂、Mo₆S₈ or MnO ₂; the electrolyte of the magnesium ion battery is mainly Grignard reagent electrolyte of ether solvent, magnesium aluminum chloride complex electrolyte or Mg-based electrolyte.

The invention has the following beneficial effects:

1. According to the invention, the aliphatic diamine modified polyetherimide membrane is used as a battery membrane, the obtained modified membrane has an exposed amino at the tail end, and the polar group is beneficial to improving the wettability and ion transmission capacity of the membrane, improving the interface performance of the battery and improving the cycle stability and rate capability of the battery. And the modified diaphragm effectively improves the combustion performance and the safety performance of the diaphragm.

The polyetherimide-aliphatic diamine diaphragm provided by the invention has higher porosity (87%), liquid absorption (456%) and high temperature resistance, and has better wettability (the contact angle is obviously reduced to 12 degrees) and ion transmission capacity.

2. The assembled battery has more stable cycle performance and multiplying power performance; the assembled lithium iron phosphate battery can stably circulate for more than 1000 cycles. The lithium ion battery is suitable for larger electrode materials, and the assembled lithium ion battery has longer cycle life and high-temperature performance; the capacity retention was 98.6% after 100 weeks of high temperature cycling at 60 ℃.

3. The polyetherimide-aliphatic diamine diaphragm provided by the invention is applied to a lithium/magnesium battery, and has a great application prospect in the aspect of developing a lithium/magnesium battery which can be used at a high temperature, is nonflammable, has better electrolyte wettability and has excellent comprehensive electrochemical performance. Meanwhile, the polyetherimide-aliphatic diamine diaphragm developed by the invention can be applied to a magnesium ion battery system, and the application field is further widened.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1: infrared spectra of PEI separator and PEI-EDA separator.

Fig. 2: infrared spectra of polyetherimide-propylene diamine diaphragm and polyetherimide-butylene diamine diaphragm.

Fig. 3: SEM images of PEI separator and PEI-EDA separator.

Fig. 4: comparison of the absorbency and porosity of Celgard 2500, PEI and PEI-EDA separators.

Fig. 5: ionic conductivity comparison of lithium ion batteries assembled using Celgard 2500, PEI and PEI-EDA separators, respectively, using application example 1.

Fig. 6: application example 2 ion mobility comparison of assembled lithium ion batteries using Celgard 2500, PEI and PEI-EDA separators, respectively.

Fig. 7: celgard 2500, PEI and PEI-EDA contact angle of the separator.

Fig. 8: ceglard 2500 thermogravimetric and DSC curves of PEI and PEI-EDA diaphragms.

Fig. 9: combustion schematic of Celgard 2500, PEI and PEI-EDA membranes.

Fig. 10: lithium ion battery using PEI-EDA separator assembled in example 3; comparative application 1 and comparative application 2 lithium ion batteries assembled using Celgard 2500, PEI as separator respectively had a 1C cycle performance at 25 ℃.

Fig. 11: lithium ion battery using PEI-EDA separator assembled in example 3; comparative application 1 and comparative application 2 impedance properties of lithium ion batteries assembled using Celgard 2500, PEI as separator at 25 ℃, respectively.

Fig. 12: lithium ion battery using PEI-EDA separator assembled in example 3; comparative application 1 and comparative application 2 lithium ion batteries assembled using Celgard 2500, PEI as separator respectively had a cycle performance of 5C at 25 ℃.

Fig. 13: lithium ion battery using PEI-EDA separator assembled in example 4; comparative application 3 and comparative application 4 lithium ion batteries assembled using Celgard 2500, PEI as separator respectively had a 1C cycle performance at 25 ℃.

Fig. 14: lithium ion battery using PEI-EDA separator assembled in example 3; comparative application 1 and comparative application 2 rate performance at 25 ℃ of lithium ion batteries assembled using Celgard 2500, PEI as separator, respectively.

Fig. 15: lithium ion battery using PEI-EDA separator assembled in example 5; comparative application 5 and comparative application 6 1C cycle performance at 25 ℃ of lithium ion batteries assembled using Celgard 2500, PEI as separator, respectively.

Fig. 16: lithium ion battery using PEI-EDA separator assembled in example 6; comparative application 7 and comparative application 8 1C cycle performance at 60 ℃ of lithium ion batteries assembled using Celgard 2500, PEI as separator, respectively.

Fig. 17: application example 7 cycling performance at 25 ℃ of magnesium ion batteries assembled with PEI-EDA separator.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without any inventive effort, are intended to be within the scope of the invention.

The polyether imide used as a raw material in the following examples in the present invention is PEI ULTEM 1000.

Example 1

The preparation of the ethylenediamine modified polyetherimide membrane (PEI-EDA) comprises the following steps:

1.12 g of polyetherimide and 0.84 of polyvinylpyrrolidone (molecular weight 1300000) of g are mixed, dissolved in 5.0 g of N, N-dimethylacetamide under heating, stirred overnight, then the mixed solution is coated on a glass plate, and then the glass plate is placed in saturated water vapor for 12s at room temperature, and then the glass plate is immersed in deionized water to solidify and remove pore-forming agents through a phase inversion method, and solidified into a film.

And soaking the dried membrane in an ethylenediamine methanol solution with the concentration of 5wt% for 9 hours, and taking out and drying to obtain the ethylenediamine chemically modified polyetherimide-ethylenediamine membrane (PEI-EDA membrane).

Example 2

Preparation of a propylene diamine modified polyetherimide membrane (PEI-PDA membrane) comprises the following steps:

1.12 g of polyetherimide and 0.84 of polyethylene glycol (molecular weight 1300000) of g are mixed, dissolved in 5.2 g of N, N-dimethylformamide under heating, stirred overnight, then the mixed solution is coated, then the mixed solution is placed in saturated water vapor for 15s at room temperature, then the mixed solution is immersed in deionized water to be solidified by a phase inversion method, the pore-forming agent is removed, and the mixed solution is solidified into a film.

After drying, soaking in an N-methylpyrrolidone solution of propylenediamine with the concentration of 8wt% for 6 hours, and drying to obtain the propylenediamine chemically modified polyetherimide-propylenediamine membrane (PEI-PDA membrane).

Example 3

Preparation of a butanediamine modified polyetherimide membrane (PEI-BDA membrane) comprises the following steps:

1.08 g of polyetherimide and 0.62 of polyvinylpyrrolidone (molecular weight 1000000) of g are mixed, dissolved in 6g of N, N-dimethylacetamide under heating, stirred overnight, then the mixed solution is coated, then the mixed solution is placed in saturated water vapor for 10s at room temperature, then the mixed solution is immersed in deionized water to solidify by a phase inversion method and remove pore-forming agent, and the mixed solution is solidified into a film.

And (3) drying the obtained membrane, soaking the membrane in ethanol solution of butanediamine with the concentration of 4wt% for 10 hours, and drying the membrane to obtain the chemically modified polyether imide-butanediamine membrane (PEI-BDA membrane).

Example 4

The preparation of the polyether imide modified by the hexamethylene diamine comprises the following steps:

1.12 g of polyetherimide and 0.84 of polyethylene glycol (molecular weight 1300000) of g are mixed, dissolved in 5.2 g of N, N-dimethylacetamide under heating, stirred overnight, then the mixed solution is coated, then the mixed solution is placed in water vapor for standing for 12s, and then immersed in deionized water for solidification and removal of pore formers.

And (3) drying the obtained film, soaking the film in an ethanol solution of hexamethylenediamine with the concentration of 6wt%, and drying for 8 hours to obtain the chemically modified polyetherimide-hexamethylenediamine diaphragm.

Example 5

The preparation method of the pentanediamine modified polyetherimide comprises the following steps:

1.47 g of polyetherimide and 0.3 of polyvinylpyrrolidone (molecular weight: 1500000) of g were mixed, dissolved in 8 g N-methylpyrrolidone under heating, stirred overnight, then the mixed solution was applied, then left to stand in water vapor for 12s, then immersed in deionized water to solidify and remove the pore-forming agent.

And (3) drying the obtained film, soaking the film in an N-methylpyrrolidone solution of which the concentration is 6wt% of that of ethylenediamine, and drying the film for 8 hours to obtain the ethylenediamine chemically modified polyetherimide-pentylene diamine diaphragm.

Example 6

The preparation method of the propylene diamine modified polyetherimide comprises the following steps:

1.31 of g of polyetherimide and 0.95 of g of polyvinylpyrrolidone (molecular weight 1000000) were mixed, dissolved in 5g of N, N-dimethylacetamide under heating, stirred overnight, then the mixed solution was applied, then left to stand in water vapor for 12s, then immersed in deionized water to solidify and remove the pore-forming agent.

And (3) drying the obtained membrane, soaking the membrane in a hexamethylenediamine methanol solution with the concentration of 6wt% and drying the membrane for 8 hours to obtain the polyether imide-propylenediamine membrane chemically modified by propylenediamine.

Assembling a polyetherimide-ethylenediamine diaphragm lithium/magnesium ion battery: the preparation of polyetherimide-ethylenediamine separator in example 1 in the invention requires the combination of the battery assembly process, lithium/magnesium ion batteries assembled with different electrolyte systems and positive electrode materials, and studies on various electrochemical properties. The following description will be made with reference to specific examples of application.

Application example 1

Assembling the steel sheet/diaphragm/steel sheet battery:

Cutting PEI-EDA diaphragm into a diaphragm with the diameter of 19 mm by a cutting machine, wherein the thickness of the diaphragm is 45 mu m; a steel sheet/membrane/steel sheet cell resembling a sandwich structure was assembled. The battery was assembled using a solution of 1M LiPF ₆ liquid electrolytes of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate (1:1:1 by volume).

Application example 2

Assembling a lithium sheet/separator/lithium sheet battery:

when the symmetric lithium ion battery was assembled, the specification and dimensions of the separator were the same as those of application example 1, and a lithium sheet/separator/lithium sheet battery similar to a sandwich structure was assembled. The battery was assembled using a solution of 1M LiPF ₆ liquid electrolytes of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate (1:1:1 by volume).

Application example 3

Assembling a lithium ion battery:

When the lithium ion battery is assembled, the specification and the size of the diaphragm are the same as those of application example 1, the positive electrode is lithium iron phosphate (LiFePO ₄), lithium iron phosphate and conductive carbon black (Super P) are uniformly mixed, polyvinylidene fluoride (PVDF) is dissolved in N-methylpyrrolidone (NMP) and the mass concentration is prepared to be 3%, then NMP solution containing PVDF is mixed with LiFePO ₄ and Super P powder and ground for 10-15 min, wherein the mass ratio of LiFePO ₄, super P and PVDF is 80:10:10, and the total mass of the weighed three is 0.1 g. And after uniformly mixing, rapidly coating the mixture on an aluminum foil with the thickness of 10 mu m, then placing the mixture in a 60 ℃ oven for drying overnight, and cutting the mixture by a cutting machine to obtain a positive plate with the diameter of 12 mm, wherein the loading amount of lithium iron phosphate on the aluminum foil is 1.5-2.1 mg cm ^-2. The lithium ion battery is assembled by using a solution of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate (volume ratio is 1:1:1) of which the liquid electrolyte of the lithium ion battery is 1M LiPF ₆, the addition amount is 100-150 mu L, and the negative electrode is lithium metal (diameter is 16 mm, thickness is 0.45 and mm).

Application example 4

Assembling a lithium ion battery:

When the lithium ion battery is assembled, the specification and the size of the diaphragm are the same as those of application example 1, the positive electrode is lithium iron phosphate, the lithium iron phosphate and Super P are uniformly mixed, polyvinylidene fluoride is dissolved in N-methylpyrrolidone to prepare the solution with the mass concentration of 3%, then NMP solution containing PVDF is mixed with LiFePO ₄ and Super P powder and ground for 10-15 min, wherein the mass ratio of the lithium iron phosphate to the Super P to the PVDF is 80:10:10, and the total mass of the weighed three is 0.1: 0.1 g. And after uniformly mixing, rapidly coating the mixture on aluminum foil with the thickness of 10 mu m, then placing the mixture in a 60 ℃ oven for drying overnight, and cutting the mixture by a cutting machine to obtain a positive plate with the diameter of 12 mm, wherein the loading amount of lithium iron phosphate on the aluminum foil is 8.0-10.0 mg cm ^-2. The lithium ion battery is assembled by using a solution of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate (volume ratio is 1:1:1) of which the liquid electrolyte of the lithium ion battery is 1M LiPF ₆, the addition amount is 100-150 mu L, and the negative electrode is lithium metal (diameter is 16 mm, thickness is 0.45 and mm).

Application example 5

Assembling a lithium ion battery:

When the lithium ion battery is assembled, the specification and the size of the separator are the same as those of application example 1, the preparation method of the positive plate is the same as that of the lithium iron phosphate positive plate in example 3, lithium cobalt oxide (LiCoO ₂) and Super P are uniformly mixed, PVDF is dissolved in NMP and the mass concentration is prepared to be 3%, then NMP solution containing PVDF is mixed with LiCoO ₂ and Super P powder and ground for 10-15 min, wherein the mass ratio of LiCoO ₂, super P and PVDF is 80:10:10, and the total mass of the weighed three is 0.1 g. And after uniformly mixing, rapidly coating the mixture on aluminum foil with the thickness of 10 mu m, then placing the mixture in a 60 ℃ oven for drying overnight, and cutting the mixture by a cutting machine to obtain a positive plate with the diameter of 12 mm, wherein the loading amount of active substances (lithium cobaltate, the same shall apply hereinafter) is 1.9-2.1 mg cm ^-2. The liquid electrolyte is selected to be 1M LiPF ₆ of ethylene carbonate/dimethyl carbonate/methyl ethyl carbonate (volume ratio is 1:1:1), the addition amount is 100-150 mu L, and the negative electrode is lithium metal (diameter is 16 mm, thickness is 0.45 and mm).

Application example 6

Assembling a lithium ion battery:

The positive plate of the lithium ion battery is prepared by replacing the solution of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate (volume ratio is 1:1:1) of the liquid electrolyte 1M LiPF ₆ of the lithium ion battery in application example 3 with the solution of propylene carbonate and diethyl carbonate (volume ratio is 3:7) of 0.5: 0.5M LiBOB, adding 110-150 mu L, and preparing the positive plate of the lithium ion battery by other steps in the same way as application example 3, wherein the active material loading amount is 1.5-2.1 mg cm ^-2. The negative electrode was lithium metal (diameter 16 mm, thickness 0.45: 0.45 mm), and a lithium ion battery was assembled.

Application example 7

Assembling a magnesium ion battery:

PEI-EDA separators were used in magnesium electrical systems. The separator was the same in size as in application example 1, and had a positive electrode of CuFeSe ₂, cuFeSe ₂ was uniformly mixed with ketjen black, and 5.5 μl of polytetrafluoroethylene emulsion (PTFE emulsion) was added. Wherein the mass ratio of CuFeSe ₂ to Super P to PVDF is 60:30:10, and the total mass of the three is 0.05: 0.05 g. The prepared CuFeSe ₂ positive electrode material was rolled and then placed in an oven at 60 ℃ to dry overnight. The loading is 0.8-1.2 mg. The magnesium ion battery was assembled using a solution of magnesium ion battery liquid electrolyte 0.4M (MgPhCl) ₂-AlCl₃ in THF with an add-on of 110-150 μl, and a negative electrode of magnesium metal (diameter 12 mm, thickness 0.093 mm).

Comparative application example 1

The lithium ion battery assembled in this comparative example was different from that in application example 3 in that the separator used was commercial Celgard 2500, and the remaining steps were the same.

Comparative application example 2

The lithium ion battery assembled in this comparative example was different from that of application example 3 in that the separator used was unmodified polyetherimide PEI, which was obtained in the middle of example 1, and the rest was the same.

Comparative application example 3

The lithium ion battery assembled in this comparative example was different from that in application example 4 in that the separator used was Celgard 2500, and the rest was the same.

Comparative application example 4

The lithium ion battery assembled in this comparative example was different from that of application example 4 in that the separator used was unmodified polyetherimide PEI, which was obtained in the middle of example 1, and the rest was the same.

Comparative application example 5

The lithium ion battery assembled in this comparative example was different from that in application example 5 in that the separator used was Celgard 2500, and the rest was the same.

Comparative application example 6

The lithium ion battery assembled in this comparative example was different from that of application example 5 in that the separator used was unmodified polyetherimide PEI, which was obtained in the middle of example 1, and the rest was the same.

Comparative application example 7

The lithium ion battery assembled in this comparative example was different from that in application example 6 in that the separator used was Celgard 2500, and the rest was the same.

Comparative application example 8

The lithium ion battery assembled in this comparative example was different from that of application example 6 in that the separator used was unmodified polyetherimide PEI, which was obtained in the middle of example 1, and the rest was the same.

The lithium/magnesium ion batteries assembled in application examples 1 to 7 and comparative application examples 1 to 8 were tested in the present invention. The PEI-EDA separator prepared according to the present invention was compared to a battery assembled using the same conditions as the purchased Celgard 2500 and PEI separator not chemically modified with ethylenediamine.

The test results were analyzed as follows:

FIG. 1 is an infrared spectrum of unmodified PEI and PEI-EDA separator obtained in example 1. The absorption peak at 3070 cm ^-1 corresponds to the stretching vibration of the C-H bond. The stretching vibration of saturated carbon hydrogen bonds is characterized by absorption at 2969 cm ^-1.2000-1550 cm^-1 as a characteristic peak of benzene and-c=o bonds. 1276 The absorption at cm ^-1 and 1102 cm ^-1 is caused by stretching vibrations of the C-O and C-O-C bonds in the PEI chain. The stretching vibration of the N-H bond of-NH ₂ and-CONH-appears at 3300 cm ^-1 of PEI-EDA diaphragm after chemical modification by ethylenediamine, which proves that ethylenediamine is successfully grafted on polyetherimide polymer, and the characteristic peak of the-C=O bond belonging to the original imide and newly generated amide in the range of 2000-1550 cm ^-1 is correspondingly enhanced and weakened.

FIG. 2 is an infrared spectrum of polyetherimide-propylene diamine (PEI-PDA) of example 2 and polyetherimide-butylene diamine (PEI-BDA) of example 3. PEI-PDA membranes and PEI-BDA membranes chemically modified with propylene diamine and butylene diamine are similar to PEI-EDA membranes, stretching vibration of the N-H bond of-NH ₂ and-CONH-occurs at 3300 cm ^-1, and the characteristic peak of the-C=O bond in the range of 2000-1550cm ^-1 is partially enhanced and attenuated.

FIG. 3 is a surface and cross-sectional SEM image of PEI and PEI-EDA membranes. Wherein, the upper three figures are the surface and cross-sectional morphology of the polyetherimide membrane that was not chemically modified with ethylenediamine, and the lower three figures are the surface and cross-sectional morphology of the polyetherimide membrane that was chemically modified with ethylenediamine. As can be seen from the SEM, the morphology of the PEI and PEI-EDA membranes is not obviously different, which indicates that the ethylenediamine does not damage the structure of the polyetherimide membrane in the chemical modification process.

FIG. 4 is a plot of the absorbency versus porosity for Celgard 2500, PEI and PEI-EDA separators. The porosity and the imbibition rate of the Celgard 2500 membrane were 54.0% and 91.0%, respectively, the porosity and the imbibition rate of the unmodified PEI membrane were 87.2% and 451.0%, respectively, and the porosity and the imbibition rate of the modified PEI-EDA membrane were 87.6% and 456.0%, respectively. In contrast, PEI-EDA separators have the highest imbibition rate.

FIG. 5 is an ion conductivity diagram of Celgard 2500, PEI and PEI-EDA separators. The battery was assembled in the same manner as in example 1, and the addition amount of the liquid electrolyte was 120. Mu.L. The ionic conductivities of Celgard 2500, PEI and PEI-EDA membranes were 0.96 mS cm ^-1、1.72 mS cm^-1 and 1.96 mS cm ^-1, respectively, at 25 ℃, indicating that the PEI-EDA membranes have higher ionic conductivities.

FIG. 6 is a graph of ion migration numbers for Celgard 2500, PEI and PEI-EDA separators. The battery was assembled in the same manner as in example 2, and the addition amount of the liquid electrolyte was 120. Mu.L. The ion migration numbers of Celgard 2500 membrane, PEI membrane and PEI-EDA membrane were 0.45, 0.55 and 0.74, respectively, at 25 ℃. PEI-EDA membranes have higher ion transfer numbers due to the chemical modification of ethylenediamine, the introduction of an additional polar functional group-NH ₂.

FIG. 7 is a schematic representation of contact angles of Celgard 2500, PEI and PEI-EDA membranes. When the electrolyte is a solution of 1.0M LiPF ₆ in EC: DMC: EMC volume ratio of 1:1:1, the contact angles of the Celgard 2500 membrane, the PEI membrane and the PEI-EDA membrane are 42.5 °, 16.9 ° and 11.9 °, respectively. The contact angle of the PEI-EDA membrane is smaller, which shows that the PEI-EDA membrane has better wettability with electrolyte.

FIG. 8 is a thermogravimetric and DSC curve of Celgard 2500, PEI and PEI-EDA diaphragms. The Celgard 2500 membrane began to lose mass at 340℃and an endothermic peak appeared in the DSC curve at 137℃to 162℃indicating that the Celgard 2500 membrane began to melt without maintaining shape integrity.

The PEI membrane starts to undergo a mass loss at 404℃due to decomposition of the residual PVP, and no significant endothermic peak appears in the PEI membrane in the DSC curve at temperatures below 400 ℃.

Mass loss started at 159 ℃ for the PEI-EDA membrane, and no significant endothermic peak appeared in the PEI-EDA membrane at temperatures below 400 ℃ in the DSC curve. Although the initial decomposition temperature of PEI-EDA membrane is lower than Celgard 2500 and PEI membrane, the melting temperature of Celgard 2500 membrane is far lower than PEI-EDA membrane, so Celgard 2500 membrane can shrink in size, but PEI-EDA membrane does not shrink at high temperature, which shows that PEI-EDA membrane has better high temperature resistance than Celgard 2500 membrane.

FIG. 9 is a schematic combustion diagram of Celgard 2500, PEI and PEI-EDA membranes. PEI-EDA separators have better flame retardant properties than Ceglard 2500 and PEI separators.

Fig. 10 is a graph showing the cycle performance of a lithium ion battery assembled with lithium iron phosphate as the positive electrode at a current density of 1C. The cycling performance comparisons at 1C rate were tested for lithium ion batteries of comparative application example 1 Celgard 2500 separator, comparative application example 2 PEI and PEI-EDA separator of application example 3. The initial capacity of the LiFePO ₄/Celgard 2500/Li battery of comparative application example 1 was 125.7 mAh g ^-1, the capacity after 500 weeks of cycling was 84.8 mAh g ^-1, and the capacity retention was 67.5%; the initial capacity of the LiFePO ₄/PEI/Li battery of comparative application example 2 was 125.7 mAh g ^-1, the capacity remaining after 500 weeks of cycling was 57.4 mAh g ^-1, and the capacity retention was 45.7%. The initial capacity of the LiFePO ₄/PEI-EDA/Li cell of application example 3 was 129.4 mAh g ^-1, the capacity remaining after 500 weeks of cycling was 108.8 mAh g ^-1, and the capacity retention was 84.1%. The battery capacity retention rate of PEI-EDA separator assembly in application example 3 was significantly higher than that of Celgard 2500 separator of comparative application example 1 and PEI separator of comparative application example 2 that was not chemically modified with ethylenediamine. The LiFePO ₄/PEI-EDA/Li battery of application example 3 has higher specific discharge capacity and better cycle stability.

FIG. 11 is a graph comparing impedance performance before and after 100 weeks of non-cycling of LiFePO ₄/Celgard 2500/LICELGARD 2500 of comparative application example 1, of a PEI/Li battery of comparative application example 2 LiFePO ₄ and of a LiFePO ₄/PEI-EDA/Li battery of application example 3, showing that the material after the ethylenediamine-modified polyetherimide separator of application example 3 exhibits lower resistance; the polyether imide diaphragm modified by ethylenediamine has higher ion transmission performance.

Fig. 12 is a graph of the cycle performance of an assembled lithium ion battery with a current density of 5C when lithium iron phosphate is the positive electrode. The cycle performance comparisons at 5C rate of the lithium ion batteries of comparative application example 1 Celgard 2500 separator, comparative application example 2 PEI separator and application example 3 PEI-EDA separator were tested. The initial capacity of the LiFePO ₄/Celgard 2500/Li battery of comparative application example 1 was 84.5 mAh g ^-1, the capacity after 800 weeks of cycling was 70.7. 70.7 mAh g ^-1, and the capacity retention was 83.7%; the initial capacity of the LiFePO ₄/PEI/Li battery of comparative application example 2 was 77.7 mAh g ^-1, the capacity remaining after 800 weeks of cycling was 46.5 mAh g ^-1, and the capacity retention was 60.0%. The initial capacity of the LiFePO ₄/PEI-EDA/Li cell of application example 3 was 90.5 mAh g ^-1, the capacity remaining after 800 weeks of cycling was 83.5 mAh g ^-1, and the capacity retention was 92.3%. The discharge capacity and the capacity retention rate of the battery assembled by the application example 3 PEI-EDA diaphragm are obviously higher than those of the battery assembled by the comparative application example 1 and the comparative application example 2, which shows that the LiFePO ₄/PEI-EDA/Li battery has higher discharge specific capacity and better cycle stability.

Fig. 13 is a graph showing the cycle performance of a lithium ion battery assembled with lithium iron phosphate as the positive electrode at a current density of 1C. Lithium ion batteries were assembled according to application example 4, and cycle performance comparisons at 1C rate were tested for Celgard 2500 separator, PEI and PEI-EDA separator assembled lithium ion batteries (corresponding to comparative application example 3 and comparative application example 4, respectively).

The initial capacity of the LiFePO ₄/Celgard 2500/Li battery of comparative application example 3 was 113.6 mAh g ^-1, the capacity after 200 weeks of cycling was 88.1 mAh g ^-1, and the capacity retention was 77.6%; the initial capacity of the LiFePO ₄/PEI/Li battery of comparative application example 4 was 109.8 mAh g ^-1, the capacity remaining after 38 weeks of cycling was 111.3 mAh g ^-1, and then a short circuit occurred. The initial capacity of the LiFePO ₄/PEI-EDA/Li cell of application example 4 was 119.5 mAh g ^-1, the capacity remaining after 200 weeks of cycling was 105.3. 105.3 mAh g ^-1, and the capacity retention was 88.1%. The discharge capacity and the capacity retention rate of the battery assembled by the PEI-EDA diaphragm are obviously higher than those of a Celgard 2500 diaphragm and a PEI diaphragm which is not chemically modified by ethylenediamine, which shows that the LiFePO ₄/PEI-EDA/Li battery of application example 4 has higher discharge specific capacity and better cycle stability.

Fig. 14 is a graph of the rate performance of a lithium ion battery assembled with lithium iron phosphate as the positive electrode. The rate performance of LiFePO ₄/Ceglard 2500/Li of application example 3, liFePO ₄/PEI/Li of comparative application example 1, and LiFePO ₄/PEI-EDA/Li of comparative application example 2 were tested, respectively. Specific capacities of LiFePO ₄/Celgard 2500/Li cells of comparative application example 2 were 145.7, 142.5, 134.5, 124.0, 109.2, 98.7, 90.6, 84.0, mAh g ^-1 at magnifications of 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, C, respectively. Specific capacities of LiFePO ₄/PEI/Li battery of comparative application example 1 were 145.4, 143.3, 134.0, 121.7, 103.5, 92.6, 83.2, 74.3 mAh g ^-1 at magnifications of 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0C, respectively. Specific capacities of LiFePO ₄/PEI-EDA/Li battery of application example 3 were 149.6, 146.5, 138.7, 128.8, 114.5, 104.6, 97.1, 91.0 and mAh g ^-1 at magnifications of 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0C, respectively. The specific capacity of the PEI-EDA separator assembled battery is higher than that of the Celgard 2500 separator and PEI separator at each multiplying power.

Fig. 15 is a cycle performance chart of a lithium ion battery assembled when lithium cobaltate is the positive electrode. The cycle performance comparisons at 1C rates of the Celgard 2500 separator of comparative application example 5, the PEI of comparative application example 6, and the PEI-EDA lithium ion battery of application example 5 were tested in accordance with application example 5. The initial capacity of the LiFePO ₄/Celgard 2500/Li battery of comparative application example 5 was 155.1 mAh g ^-1, the capacity after 150 weeks of cycling was 118.0mAh g ^-1, and the capacity retention was 76.1%. The initial capacity of the LiFePO ₄/PEI/Li battery of comparative application example 6 was 143.2 mAh g ^-1, the capacity remaining after 150 weeks of cycling was 113.2 mAh g ^-1, and the capacity retention was 79.1%. The initial capacity of the LiFePO ₄/PEI-EDA/Li battery of application example 5 was 155.2 mAh g ^-1, the capacity remaining after 150 weeks of cycling was 138.1. 138.1 mAh g ^-1, and the capacity retention was 89.0%. The cycle stability and capacity retention rate of the PEI-EDA membrane assembled battery are obviously higher than those of PEI membranes and Celgard 2500 membranes which are not chemically modified by ethylenediamine, and the LiCoO ₂/PEI-EDA/Li battery has better cycle stability.

Fig. 16 is a graph showing the cycle performance of an assembled lithium ion battery at a high temperature of 60 c when lithium iron phosphate is the positive electrode. The lithium ion battery was assembled as in application example 6, and the Celgard 2500 separator of comparative application example 7, the PEI separator of comparative application example 8 and the cycle performance of the application example 6 PEI-EDA lithium ion battery at a rate of 1C were tested for comparison. The initial capacity of the LiFePO ₄/Celgard 2500/Li battery of comparative application example 7 was 144.0 mAh g ^-1, the capacity remaining after 100 weeks of cycling was 134.0. 134.0 mAh g ^-1, and the capacity retention was 93.1%. The initial capacity of the LiFePO ₄/PEI/Li battery of comparative application example 8 was 144.0 mAh g ^-1, the capacity after 6 weeks of cycling was 137 mAh g ^-1, after which the battery was short circuited and no charge and discharge could be performed normally. The initial capacity of the LiFePO ₄/PEI-EDA/Li cell of application example 6 was 149.5 mAh g ^-1, the capacity remaining after 100 weeks of cycling was 147.4. 147.4 mAh g ^-1, and the capacity retention was 98.6%. The battery cycle stability and capacity retention rate of PEI-EDA diaphragm assembly are obviously higher than those of a polyetherimide diaphragm and a Celgard 2500 diaphragm which are not chemically modified by ethylenediamine, and the battery has better high-temperature cycle stability.

Fig. 17 is a graph showing the cycling performance of a magnesium ion battery assembled at 25 c with CuFeSe ₂ as the positive electrode. PEI-EDA separator A magnesium ion battery was assembled according to the procedure of application example 7 with a loading of active material (CuFeSe ₂, hereinafter the same) of 0.9-1.1 mg. The addition amount of the liquid electrolyte was 120. Mu.L. The cycling performance of PEI-EDA separators at 0.05A g ^-1 current in magnesium ion batteries was tested. The results show that PEI-EDA membrane can be applied to a magnesium ion battery system.

The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.

Claims

1. A method for preparing a polyetherimide diaphragm chemically modified with a fatty diamine, characterized in that it comprises the following steps:

(1) dissolving polyetherimide and a pore-forming agent in an organic solvent to form a casting solution, curing the casting solution into a film by a phase inversion method, and then drying to obtain a polyetherimide film;

(2) Immersing the polyetherimide membrane of step (1) in a fatty diamine solution, and then drying to obtain a polyetherimide membrane chemically modified with fatty diamine.

2. The method for preparing a polyetherimide diaphragm chemically modified with fatty diamine according to claim 1, characterized in that: in the step (1), the pore-forming agent is polyvinyl pyrrolidone or polyethylene glycol, and the molecular weight of the pore-forming agent is 1 million to 1.5 million; and the organic solvent is N,N-dimethylacetamide, N,N-dimethylformamide or N-methylpyrrolidone.

3. The method for preparing a polyetherimide diaphragm chemically modified with aliphatic diamine according to claim 1 or 2, characterized in that: in the step (1), the concentration of the polyetherimide in the casting solution is 14-18wt%, and the concentration of the pore-forming agent in the casting solution is 3-13wt%.

4. The method for preparing a polyetherimide diaphragm chemically modified with aliphatic diamine according to claim 3, characterized in that: in the step (1), the concentration of the polyetherimide in the casting solution is 15-16wt%; the concentration of the pore-forming agent in the casting solution is 8-12wt%.

5. The method for preparing a polyetherimide diaphragm chemically modified with aliphatic diamine according to claim 3, characterized in that the aliphatic diamine in step (2) is ethylenediamine, propylenediamine, butylenediamine, pentamethylenediamine or hexamethylenediamine.

6. The method for preparing a polyetherimide diaphragm chemically modified with fatty diamine according to claim 5, characterized in that: in the step (2), the concentration of the fatty diamine in the solution is 4-8wt%; the time for the polyetherimide to be immersed in the fatty diamine solution is 6-10h; and the solvent of the fatty diamine solution is methanol, N-methylpyrrolidone or ethanol.

7. A polyetherimide membrane chemically modified with fatty diamine prepared according to the method of any one of claims 1 to 6, characterized in that the polyetherimide chemically modified with fatty diamine has a structural unit represented by the general formula (I):

General formula (I)

Where m=1, 1.5, 2, 2.5 or 3.

8 . The polyetherimide membrane chemically modified with aliphatic diamine according to claim 7 , wherein the thickness of the polyetherimide membrane chemically modified with aliphatic diamine is 30-60 μm.

9. Use of the polyetherimide separator chemically modified with aliphatic diamine according to claim 7 or 8 in lithium ion batteries.

10. Use of the polyetherimide diaphragm chemically modified with aliphatic diamine according to claim 7 or 8 in a magnesium ion battery.