A fatty diamine chemically modified polyetherimide separator, its preparation method and application in lithium / magnesium batteries

Abstract

The application provides a kind of fat diamine chemically modified polyetherimide diaphragm and its preparation method and application in lithium / magnesium battery.Polyetherimide and pore-forming agent are dissolved in organic solvent to form casting solution, the casting solution is solidified into film by phase inversion method, and then dried to obtain polyetherimide film; the polyetherimide film is immersed in fat diamine solution, and then dried to obtain fat diamine chemically modified polyetherimide diaphragm.The obtained fat diamine chemically modified polyetherimide diaphragm is rich in polar groups, has moderate and uniform pore size, high porosity, small contact angle, strong ion transmission capacity, effectively improves the thermal stability of diaphragm and the interface performance of battery, can be assembled with various electrode materials, and the assembled lithium ion battery and magnesium ion battery have better cycle stability than commercial polyolefin diaphragm.

Description

Technical Field

[0001] This invention belongs to the field of lithium / magnesium ion battery separators, specifically relating to a polyetherimide separator chemically modified with aliphatic diamine, its preparation method, and its application in lithium / magnesium batteries. Background Technology

[0002] Batteries, as a new generation of green, high-energy-density devices, play a crucial role in the field of new energy storage and are widely used in electronic products, electric vehicles, and other areas. A battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. Among these, the separator is of paramount importance for the composition and safety of lithium / magnesium-ion batteries. On the one hand, the separator separates the positive and negative electrodes, preventing direct contact and short circuits that could lead to safety accidents. On the other hand, the porous structure inside the separator allows metal ions in the electrolyte to migrate freely between the electrodes. Currently, commercially available separators are mainly based on polyolefin materials. While these separators possess good mechanical properties and electrochemical stability, they also suffer from drawbacks such as low melting points, poor thermal stability, and limited electrolyte compatibility due to poor wettability. Therefore, developing novel, non-flammable, and electrolyte-friendly battery separators that can be used at high temperatures is crucial.

[0003] Polyetherimide (PEI), as an engineering plastic, possesses high strength, rigidity, abrasion resistance, and dimensional stability. It also exhibits a wide range of chemical resistance, including resistance to most hydrocarbons, alcohols, inorganic acids, and all halogenated solvents. Furthermore, polyetherimide contains many polar groups, resulting in better electrolyte wettability. Patent CN109860483A discloses a polyetherimide coating solution, a coating base film, its fabrication method, and its application in secondary batteries. While this method maximizes the preservation of the original stability of the polyetherimide solution and provides good thermal shrinkage properties to the membrane coating solution through the addition of inorganic particles, the coating method easily clogs the pores of the base film, hindering ion transport and thus affecting battery performance. Patent CN106876630A provides a cross-linked polyetherimide porous membrane applied to lithium-ion batteries, exhibiting better mechanical properties and thermal stability. This patent utilizes a humidity-controlled phase inversion method to obtain a polyetherimide separator, then uses p-phenylenediamine as a crosslinking agent. By adjusting the crosslinking time, a crosslinked polyetherimide porous separator is obtained. This separator has a porosity of approximately 50-75% and a contact angle of 39-50º. The assembled lithium-ion battery can operate for 55-200 cycles. However, the modified polyetherimide described in this patent suffers from problems such as low porosity, poor wettability with electrolyte, and inability to achieve long-term stable cycling. Summary of the Invention

[0004] To address the technical problems existing in the prior art, this invention proposes a polyetherimide (PEI) separator chemically modified with aliphatic diamine, its preparation method, and its application in lithium / magnesium batteries. The porous PEI separator obtained by this invention has large and continuous pores. Then, the PEI separator is structurally modified with aliphatic diamine of lower molecular weight without completely forming a cross-linked structure, effectively improving the wettability and ion transport capacity of the separator, thereby improving the cycle stability and safety of lithium / magnesium batteries.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A method for preparing a polyetherimide separator chemically modified with aliphatic diamine includes the following steps:

[0007] (1) Polyetherimide and pore-forming agent are dissolved in organic solvent I to form a casting solution. The casting solution is cured into a film by phase inversion and then dried to obtain a polyetherimide film.

[0008] (2) Immerse the polyetherimide membrane from step (1) in a fatty diamine solution and then dry it to obtain a fatty diamine chemically modified polyetherimide membrane.

[0009] The resulting modified separator has terminally exposed amino groups, which contribute to improving the separator's wettability and ion transport capacity, enhancing the battery's interfacial performance, and improving its cycle stability and rate performance. Furthermore, this modified separator effectively improves the separator's combustion performance and safety performance.

[0010] In step (1), the pore-forming agent is polyvinylpyrrolidone or polyethylene glycol, and the molecular weight of the pore-forming agent is 1,000,000 to 1,500,000; the organic solvent I is N,N-dimethylacetamide, N,N-dimethylformamide or N-methylpyrrolidone.

[0011] In step (1), the concentration of polyetherimide in the casting solution is 14-18 wt%, preferably 15-16 wt%; the concentration of the pore-forming agent in the casting solution is 3-13 wt%, preferably 8-12 wt%; at this time, the membrane pores are most uniform and interconnected, the contact angle of the prepared PEI membrane is the smallest, and the porosity is the largest; the molecular weight and concentration of the pore-forming agent affect the porosity.

[0012] In step (1), the phase transformation method involves scraping the casting solution into a film, then placing it in saturated water vapor and letting it stand for 10-15 seconds, and then immersing it in deionized water to solidify and remove the pore-forming agent.

[0013] In step (2), the concentration of the aliphatic diamine in the solution is 4-8 wt%; the soaking time of the polyetherimide in the aliphatic diamine solution is 6-10 h; the solvent of the aliphatic diamine solution is methanol, ethanol or N-methylpyrrolidone; the aliphatic diamine in the step is ethylenediamine, propylenediamine, butanediamine, pentanediamine or hexamethylenediamine.

[0014] The aliphatic diamine-modified polyetherimide has the structural unit shown in general formula (I):

[0015] General Formula (I)

[0016] Where m = 1, 1.5, 2, 2.5 or 3.

[0017] The thickness of the aliphatic diamine-modified polyetherimide separator is 30-60 μm, preferably 40-45 μm.

[0018] The application of the aliphatic diamine chemically modified polyetherimide separator in a battery, wherein the battery is a lithium-ion battery or a magnesium-ion battery.

[0019] The lithium-ion battery includes a positive electrode material, a negative electrode material, an electrolyte, and a battery separator. The positive electrode material includes anionic, layered oxide, or organic electrode materials. The anionic type is lithium iron phosphate, lithium manganese phosphate, or other polyanionic materials. The layered oxide type is lithium cobalt oxide or lithium manganese oxide. The organic electrode material is a ternary material or Prussian blue. The negative electrode material is selected from any one of lithium metal, alloy compounds, metal oxides, metal sulfides, metal phosphides, carbon materials, layered compounds, or organic materials. The alloy compound is two or more of tin, aluminum, bismuth, antimony, or zinc metal compounds. The metal oxide is TiO2. The metal sulfide is FeS, SnS, SnS2, or FeS2. The metal phosphide is Sn3P4. The carbon material is hard carbon or soft carbon. The layered compound is graphite, MXene, MoS2, or black phosphorus. The organic material is polyimide or polybenzoquinone.

[0020] Magnesium-ion batteries include positive electrode materials, negative electrode materials, electrolytes, and battery separators. The positive electrode materials of magnesium-ion batteries include CuFeSe2, Mo6S8, or MnO2. The electrolytes of magnesium-ion batteries are mainly Grignard reagent electrolytes with ether solvents, magnesium aluminum chloride complex electrolytes, or Mg-based electrolytes.

[0021] The present invention has the following beneficial effects:

[0022] 1. In this invention, a polyetherimide separator modified with aliphatic diamine is used as the battery separator. The resulting modified separator has terminal exposed amino groups, which help improve the wettability and ion transport capacity of the separator, improve the interfacial performance of the battery, and enhance the cycle stability and rate performance of the battery. Furthermore, this modified separator effectively improves the combustion performance and safety performance of the separator.

[0023] The polyetherimide-aliphatic diamine membrane of the present invention exhibits higher porosity (87%), liquid absorption rate (456%) and high temperature resistance, as well as better wettability (contact angle significantly reduced to 12º) and ion transport capability.

[0024] 2. The battery assembled in this application has more stable cycle performance and rate performance; the assembled lithium iron phosphate battery can stably cycle for more than 1000 cycles. With the adaptation of larger electrode materials, the assembled lithium-ion battery has a longer cycle life and high-temperature performance; after 100 cycles at 60°C, the capacity retention rate is 98.6%.

[0025] 3. Applying the polyetherimide-aliphatic diamine separator of this invention to lithium / magnesium batteries shows great promise in developing lithium / magnesium batteries that can be used at high temperatures, are non-flammable, have better electrolyte wettability, and exhibit excellent overall electrochemical performance. Furthermore, the polyetherimide-aliphatic diamine separator developed in this invention can be applied to magnesium-ion battery systems, further broadening its application scope. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 Infrared spectra of PEI membrane and PEI-EDA membrane.

[0028] Figure 2 Infrared spectra of polyetherimide-propylenediamine membrane and polyetherimide-butylenediamine membrane.

[0029] Figure 3 SEM images of PEI diaphragm and PEI-EDA diaphragm.

[0030] Figure 4 Comparison of liquid absorption rate and porosity of Celgard 2500, PEI and PEI-EDA membranes.

[0031] Figure 5Application Example 1: Comparison of ionic conductivity of lithium-ion batteries assembled using Celgard 2500, PEI, and PEI-EDA separators, respectively.

[0032] Figure 6 Application Example 2: Comparison of ion transference numbers of lithium-ion batteries assembled using Celgard 2500, PEI, and PEI-EDA separators, respectively.

[0033] Figure 7 Contact angles of Celgard 2500, PEI, and PEI-EDA membranes.

[0034] Figure 8 Thermogravimetric and DSC curves of Ceglard 2500, PEI and PEI-EDA separators.

[0035] Figure 9 Schematic diagram of combustion of Celgard 2500, PEI and PEI-EDA membranes.

[0036] Figure 10 The lithium-ion battery with PEI-EDA separator assembled in Application Example 3; the 1C cycle performance of lithium-ion batteries assembled with Celgard 2500 and PEI separators respectively in Application Example 1 and Application Example 2 at 25°C.

[0037] Figure 11 Lithium-ion batteries assembled with PEI-EDA separators in Application Example 3; and the impedance performance of lithium-ion batteries assembled with Celgard 2500 and PEI separators respectively in Application Example 1 and Application Example 2 at 25°C.

[0038] Figure 12 The lithium-ion battery with PEI-EDA separator assembled in Application Example 3; the 5C cycle performance of lithium-ion batteries assembled with Celgard 2500 and PEI separators respectively in Application Example 1 and Application Example 2 at 25°C.

[0039] Figure 13 The lithium-ion battery assembled with the PEI-EDA separator in Application Example 4; the 1C cycle performance of lithium-ion batteries assembled with Celgard 2500 and PEI separators respectively in Application Example 3 and Application Example 4 at 25°C.

[0040] Figure 14 Application Example 3: Lithium-ion battery with PEI-EDA separator assembled; Comparative Application Example 1 and Comparative Application Example 2: Lithium-ion batteries assembled with Celgard 2500 and PEI separators, respectively, at 25°C, show rate performance.

[0041] Figure 15 The lithium-ion battery with the PEI-EDA separator assembled in Application Example 5 was compared with the lithium-ion batteries assembled with Celgard 2500 and PEI separators respectively at 25°C for 1 C cycle performance.

[0042] Figure 16 The lithium-ion battery assembled with the PEI-EDA separator in Application Example 6; the 1C cycle performance of lithium-ion batteries assembled with Celgard 2500 and PEI separators respectively in Application Example 7 and Application Example 8 at 60°C.

[0043] Figure 17 Application Example 7: Cycle performance of a magnesium-ion battery equipped with a PEI-EDA separator at 25°C. Detailed Implementation

[0044] 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, and 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.

[0045] In the following embodiments of the present invention, the raw material polyetherimide is of type PEI ULTEM 1000.

[0046] Example 1

[0047] The preparation steps of an ethylenediamine-modified polyetherimide membrane (PEI-EDA) are as follows:

[0048] 1.12 g of polyetherimide and 0.84 g of polyvinylpyrrolidone (molecular weight 1,300,000) were mixed and dissolved in 5.0 g of N,N-dimethylacetamide under heating conditions. The mixture was stirred overnight. The solution was then coated onto a glass plate and left to stand in saturated water vapor at room temperature for 12 seconds. The plate was then immersed in deionized water to solidify by phase inversion and remove the pore-forming agent, thus curing the film.

[0049] The dried membrane was immersed in a 5 wt% ethylenediamine methanol solution for 9 hours, and then removed and dried to obtain the ethylenediamine chemically modified polyetherimide-ethylenediamine membrane (PEI-EDA membrane).

[0050] Example 2

[0051] The preparation steps of a propylene diamine-modified polyetherimide membrane (PEI-PDA membrane) are as follows:

[0052] 1.12 g of polyetherimide and 0.84 g of polyethylene glycol (molecular weight 1,300,000) were mixed and dissolved in 5.2 g of N,N-dimethylformamide under heating conditions. The mixture was stirred overnight, and then the mixture was applied to a coating. The coating was then placed in saturated water vapor at room temperature for 15 seconds. Finally, the coating was immersed in deionized water to solidify by phase inversion and remove the pore-forming agent, thus curing the film.

[0053] After drying, the membrane is soaked in an 8 wt% N-methylpyrrolidone solution of propylenediamine for 6 hours and then dried to obtain a propylenediamine-modified polyetherimide-propylenediamine membrane (PEI-PDA membrane).

[0054] Example 3

[0055] The preparation steps of a butadiamine-modified polyetherimide membrane (PEI-BDA membrane) are as follows:

[0056] 1.08 g of polyetherimide and 0.62 g of polyvinylpyrrolidone (molecular weight 1,000,000) were mixed and dissolved in 6 g of N,N-dimethylacetamide under heating conditions. The mixture was stirred overnight, and then the mixture was applied to a coating. The coating was then placed in saturated water vapor at room temperature for 10 seconds. Finally, the coating was immersed in deionized water to solidify by phase inversion and remove the pore-forming agent, thus curing the film.

[0057] After drying, the obtained membrane was soaked in an ethanol solution of 4 wt% butanediamine for 10 h and then dried to obtain a butanediamine-modified polyetherimide-butanediamine membrane (PEI-BDA membrane).

[0058] Example 4

[0059] The preparation steps of a hexamethylenediamine-modified polyetherimide are as follows:

[0060] Mix 1.12 g of polyetherimide and 0.84 g of polyethylene glycol (molecular weight 1,300,000), dissolve in 5.2 g of N,N-dimethylacetamide under heating, stir overnight, then apply the mixture, place it in steam for 12 seconds, then immerse it in deionized water to solidify and remove the pore-forming agent.

[0061] After drying, the resulting membrane was immersed in a 6 wt% hexamethylenediamine ethanol solution and then dried for 8 hours to obtain a hexamethylenediamine chemically modified polyetherimide-hexamethylenediamine membrane.

[0062] Example 5

[0063] The preparation steps of a pentanediamine-modified polyetherimide are as follows:

[0064] 1.47 g of polyetherimide and 0.3 g of polyvinylpyrrolidone (molecular weight 1,500,000) were mixed and dissolved in 8 g of N-methylpyrrolidone under heating conditions. The mixture was stirred overnight, then applied to the surface and left to stand in steam for 12 seconds. The mixture was then immersed in deionized water to solidify and remove the pore-forming agent.

[0065] After drying, the resulting membrane was immersed in a 6 wt% N-methylpyrrolidone solution of pentanediamine and then dried for 8 hours to obtain an ethylenediamine-modified polyetherimide-pentanediamine membrane.

[0066] Example 6

[0067] The preparation steps of a propylene diamine-modified polyetherimide are as follows:

[0068] Mix 1.31 g of polyetherimide and 0.95 g of polyvinylpyrrolidone (molecular weight 1,000,000), dissolve in 5 g of N,N-dimethylacetamide under heating conditions, stir overnight, then apply the mixture, place it in steam for 12 seconds, then immerse it in deionized water to solidify and remove the pore-forming agent.

[0069] After drying, the resulting membrane was soaked in a 6 wt% hexamethylenediamine methanol solution and then dried for 8 hours to obtain a propylenediamine chemically modified polyetherimide-propylenediamine membrane.

[0070] Assembly of polyetherimide-ethylenediamine (PED) membrane lithium / magnesium ion batteries: This invention, using the polyetherimide-ethylenediamine (PED) membrane prepared in Example 1, requires consideration of the battery assembly process during preparation. Lithium / magnesium ion batteries assembled with different electrolyte systems and cathode materials are studied, and various electrochemical performances are investigated. Specific application examples are provided below.

[0071] Application Example 1

[0072] Assemble steel sheet / separator / steel sheet batteries:

[0073] The PEI-EDA separator was cut into 19 mm diameter pieces with a thickness of 45 μm using a cutting machine; a steel sheet / separator / steel sheet battery with a sandwich-like structure was assembled. The lithium-ion battery liquid electrolyte was a 1 M LiPF6 solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (volume ratio 1:1:1) to assemble the battery.

[0074] Application Example 2

[0075] Assemble lithium-ion cells / separator / lithium-ion batteries:

[0076] When assembling a symmetrical lithium-ion battery, the separator dimensions are the same as in Application Example 1, and a lithium-cell / separator / lithium-cell battery with a sandwich structure is assembled. The lithium-ion battery liquid electrolyte is a 1 M LiPF6 solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (volume ratio 1:1:1) to assemble the battery.

[0077] Application Example 3

[0078] Assemble lithium-ion batteries:

[0079] When assembling lithium-ion batteries, the separator dimensions are the same as in Application Example 1. The positive electrode is lithium iron phosphate (LiFePO4). LiFePO4 is mixed uniformly with conductive carbon black (Super P). Polyvinylidene fluoride (PVDF) is dissolved in N-methylpyrrolidone (NMP) to prepare a solution with a mass concentration of 3%. Then, the NMP solution containing PVDF is mixed with the powdered LiFePO4 and Super P and ground for 10-15 min. The mass ratio of LiFePO4, Super P, and PVDF is 80:10:10, and the total mass of the three components is 0.1 g. After mixing, it is quickly coated onto an aluminum foil with a thickness of 10 μm and then dried overnight in an oven at 60 °C. Positive electrode sheets with a diameter of 12 mm are obtained using a cutting machine. The loading of lithium iron phosphate on the aluminum foil is 1.5-2.1 mg / cm³. -2 The lithium-ion battery uses a 1 M LiPF6 solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (volume ratio 1:1:1) at a concentration of 100-150 μL. The negative electrode is metallic lithium (16 mm in diameter and 0.45 mm in thickness) to assemble the lithium-ion battery.

[0080] Application Example 4

[0081] Assemble lithium-ion batteries:

[0082] When assembling lithium-ion batteries, the separator dimensions are the same as in Application Example 1. The positive electrode is lithium iron phosphate. Lithium iron phosphate and Super P are mixed evenly. Polyvinylidene fluoride is dissolved in N-methylpyrrolidone to prepare a concentration of 3%. Then, an NMP solution containing PVDF is mixed with LiFePO4 and Super P powder and ground for 10-15 min. The mass ratio of lithium iron phosphate, Super P, and PVDF is 80:10:10, and the total mass of the three is 0.1 g. After mixing, it is quickly coated onto a 10 μm thick aluminum foil and then dried overnight in a 60 °C oven. Positive electrode sheets with a diameter of 12 mm are obtained using a cutting machine. The lithium iron phosphate loading on the aluminum foil is 8.0-10.0 mg / cm³. -2The lithium-ion battery uses a 1M LiPF6 solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (volume ratio 1:1:1) at a concentration of 100-150 μL. The negative electrode is metallic lithium (16 mm in diameter and 0.45 mm in thickness) to assemble the lithium-ion battery.

[0083] Application Example 5

[0084] Assemble lithium-ion batteries:

[0085] When assembling lithium-ion batteries, the separator dimensions are the same as in Application Example 1. The preparation of the positive electrode is the same as that of the lithium iron phosphate positive electrode in Example 3. Lithium cobalt oxide (LiCoO2) and Super P are mixed evenly. PVDF is dissolved in NMP to prepare a solution with a mass concentration of 3%. Then, the NMP solution containing PVDF is mixed with the powders of LiCoO2 and Super P and ground for 10-15 min. The mass ratio of LiCoO2, Super P, and PVDF is 80:10:10, and the total mass of the three is 0.1 g. After mixing, it is quickly coated onto an aluminum foil with a thickness of 10 μm and then dried overnight in a 60 ℃ oven. The positive electrode is then cut with a cutting machine to obtain a diameter of 12 mm, with an active material (lithium cobalt oxide, the same below) loading of 1.9-2.1 mg cm⁻¹. -2 The selected liquid electrolyte was a 1 M LiPF6 solution of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (volume ratio 1:1:1), with an addition amount of 100-150 μL. The negative electrode was lithium metal (16 mm in diameter and 0.45 mm in thickness).

[0086] Application Example 6

[0087] Assemble lithium-ion batteries:

[0088] The lithium-ion battery liquid electrolyte solution of 1 M LiPF6 (ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1) in Application Example 3 was replaced with a 0.5 M LiBOB solution of propylene carbonate and diethyl carbonate in a volume ratio of 3:7, with an addition volume of 110-150 μL. The other steps were the same as in Application Example 3 to prepare the positive electrode sheet for the lithium-ion battery, wherein the active material loading was 1.5-2.1 mg cm⁻¹. -2 The negative electrode is metallic lithium (16 mm in diameter and 0.45 mm in thickness), which is used to assemble a lithium-ion battery.

[0089] Application Example 7

[0090] Assemble magnesium-ion batteries:

[0091] PEI-EDA membranes were used in a magnesium-ion battery system. The membrane dimensions were the same as in Application Example 1. The positive electrode was CuFeSe2, which was uniformly mixed with Ketjen black and 5.5 μL of polytetrafluoroethylene (PTFE) emulsion was added. The mass ratio of CuFeSe2, Super P, and PVDF was 60:30:10, and the total mass of the three components was 0.05 g. The prepared CuFeSe2 positive electrode material was rolled and then dried overnight in a 60 °C oven. The loading was 0.8–1.2 mg. The liquid electrolyte for the magnesium-ion battery was a 0.4 M (MgPhCl)2-AlCl3 solution in THF, added in an amount of 110–150 μL. The negative electrode was metallic magnesium (12 mm in diameter and 0.093 mm in thickness), and a magnesium-ion battery was assembled.

[0092] Comparative Application Example 1

[0093] The lithium-ion battery assembled in this comparative example differs from that in Application Example 3 in that the separator used is the commercial Celgard 2500; the other steps are the same.

[0094] Comparative Application Example 2

[0095] The lithium-ion battery assembled in this comparative example differs from that in Application Example 3 in that the separator used is unmodified polyetherimide (PEI), which is the same as the unmodified polyetherimide (PEI) obtained in the intermediate process of Example 1.

[0096] Comparative Application Example 3

[0097] The lithium-ion battery assembled in this comparative example differs from that in Application Example 4 in that it uses a Celgard 2500 separator; otherwise, they are the same.

[0098] Comparative Application Example 4

[0099] The lithium-ion battery assembled in this comparative example differs from that in Application Example 4 in that the separator used is unmodified polyetherimide (PEI), which is the same as the unmodified polyetherimide (PEI) obtained in the intermediate process of Example 1.

[0100] Comparative Application Example 5

[0101] The lithium-ion battery assembled in this comparative example differs from that in Application Example 5 in that it uses Celgard 2500 separator; otherwise, they are the same.

[0102] Comparative Application Example 6

[0103] The lithium-ion battery assembled in this comparative example differs from that in Application Example 5 in that the separator used is unmodified polyetherimide (PEI), which is the same as the unmodified polyetherimide (PEI) obtained in the intermediate process of Example 1.

[0104] Comparative Application Example 7

[0105] The lithium-ion battery assembled in this comparative example differs from that in Application Example 6 in that it uses a Celgard 2500 separator; otherwise, they are the same.

[0106] Comparative Application Example 8

[0107] The lithium-ion battery assembled in this comparative example differs from that in Application Example 6 in that the separator used is unmodified polyetherimide (PEI), which is the same as the unmodified polyetherimide (PEI) obtained in the intermediate process of Example 1.

[0108] The lithium / magnesium ion batteries assembled with the corresponding examples 1-7 and comparative application examples 1-8 of this invention were tested. Batteries assembled with the PEI-EDA separator prepared according to this invention were compared with those assembled with purchased Celgard 2500 and PEI separators without ethylenediamine chemical modification under the same conditions.

[0109] The test results are analyzed as follows:

[0110] Figure 1 Infrared spectra of unmodified PEI and the PEI-EDA membrane obtained in Example 1. At 3070 cm⁻¹ -1 The absorption peak at [value] corresponds to the stretching vibration of the =CH bond. The stretching vibration of a saturated C-H bond is at 2969 cm⁻¹. -1 2000-1550 cm -1 The absorption at 1276 cm⁻¹ is a characteristic peak for benzene and the -C=O bond. -1 and 1102 cm -1 The absorption at this point is caused by the stretching vibrations of the CO and COC bonds in the PEI chain. The PEI-EDA membrane, chemically modified with ethylenediamine, was subjected to [a specific absorption] at 3300 cm⁻¹. -1 The presence of stretching vibrations of the NH bonds in the -NH2 and -CONH- regions at the 2000-1550 cm⁻¹ indicates that ethylenediamine was successfully grafted onto the polyetherimide polymer, and the results demonstrate that ethylenediamine was successfully grafted onto the polyetherimide polymer. -1 Within the range, the characteristic peaks of the -C=O bonds belonging to the original imide and the newly formed amide show corresponding enhancement and weakening.

[0111] Figure 2The infrared spectra of polyetherimide-propylenediamine (PEI-PDA) from Example 2 and polyetherimide-butylenediamine (PEI-BDA) from Example 3 are shown. The PEI-PDA and PEI-BDA membranes, chemically modified with propylenediamine and butylenediamine respectively, are similar to the PEI-EDA membrane, showing infrared spectra at 3300 cm⁻¹. -1 Stretching vibrations of the NH bonds in -NH2 and -CONH- occur at 2000-1550 cm⁻¹. -1 The characteristic peaks of the -C=O bond within the range show some enhancement and some weakening.

[0112] Figure 3 SEM images of the surface and cross-section of PEI and PEI-EDA membranes are shown. The top three images show the surface and cross-sectional morphology of the polyetherimide membrane without ethylenediamine chemical modification, while the bottom three images show the surface and cross-sectional morphology of the polyetherimide membrane with ethylenediamine chemical modification. The SEM images show no significant difference in morphology between the PEI and PEI-EDA membranes, indicating that ethylenediamine did not damage the structure of the polyetherimide membrane during the chemical modification process.

[0113] Figure 4 This chart compares the liquid absorption rate and porosity of Celgard 2500, PEI, and PEI-EDA membranes. The Celgard 2500 membrane has a porosity of 54.0% and a liquid absorption rate of 91.0%, while the unmodified PEI membrane has a porosity of 87.2% and a liquid absorption rate of 451.0%. The modified PEI-EDA membrane has a porosity of 87.6% and a liquid absorption rate of 456.0%. Comparatively, the PEI-EDA membrane exhibits the highest liquid absorption rate.

[0114] Figure 5 The diagram shows the ionic conductivity of the Celgard 2500, PEI, and PEI-EDA membranes. The battery was assembled according to the steps in Example 1, with 120 μL of liquid electrolyte added. At 25°C, the ionic conductivity of the Celgard 2500, PEI, and PEI-EDA membranes were 0.96 mS / cm. -1 1.72 mS cm -1 and 1.96 mS cm -1 This indicates that the PEI-EDA membrane has higher ionic conductivity.

[0115] Figure 6The diagram shows the ion transference numbers of the Celgard 2500, PEI, and PEI-EDA membranes. The battery was assembled according to the steps in Example 2, with 120 μL of liquid electrolyte added. At 25°C, the ion transference numbers of the Celgard 2500, PEI, and PEI-EDA membranes were 0.45, 0.55, and 0.74, respectively. The PEI-EDA membrane exhibited a higher ion transference number due to the introduction of the additional polar functional group -NH2 through ethylenediamine chemical modification.

[0116] Figure 7 This diagram illustrates the contact angles of Celgard 2500, PEI, and PEI-EDA membranes. When the electrolyte is a 1.0 M LiPF6 solution in an EC:DMC:EMC volume ratio of 1:1:1, the contact angles of the Celgard 2500 membrane, PEI membrane, and PEI-EDA membrane are 42.5°, 16.9°, and 11.9°, respectively. The smaller contact angle of the PEI-EDA membrane indicates better wettability with the electrolyte.

[0117] Figure 8 The thermogravimetric and DSC curves of Celgard 2500, PEI, and PEI-EDA membranes are shown. The Celgard 2500 membrane begins to lose mass at 340℃, and an endothermic peak appears in the DSC curve between 137℃ and 162℃, indicating that the Celgard 2500 membrane begins to melt and cannot maintain its shape.

[0118] The PEI membrane begins to lose mass at 404℃ due to the decomposition of residual PVP. In the DSC curve, no obvious endothermic peak is observed in the PEI membrane at temperatures below 400℃.

[0119] The PEI-EDA membrane began to experience mass loss at 159℃, and no significant endothermic peak was observed in the DSC curve below 400℃. Although the initial decomposition temperature of the PEI-EDA membrane was lower than that of Celgard 2500 and PEI membranes, the melting temperature of the Celgard 2500 membrane was much lower than that of the PEI-EDA membrane. Therefore, the Celgard 2500 membrane experienced dimensional shrinkage, while the PEI-EDA membrane did not shrink at high temperatures, indicating that the PEI-EDA membrane had better high-temperature resistance than the Celgard 2500 membrane.

[0120] Figure 9 This diagram illustrates the combustion of Celgard 2500, PEI, and PEI-EDA membranes. The PEI-EDA membrane exhibits better flame-retardant properties compared to Celgard 2500 and PEI membranes.

[0121] Figure 10 This diagram shows the cycle performance of a lithium-ion battery assembled with lithium iron phosphate as the cathode at a current density of 1 C. The cycle performance of lithium-ion batteries using the Celgard 2500 separator (Comparative Application Example 1), the PEI separator (Comparative Application Example 2), and the PEI-EDA separator (Comparative Application Example 3) at 1 C rate was compared. The initial capacity of the LiFePO4 / Celgard 2500 / Li battery in Comparative Application Example 1 was 125.7 mAh g⁻¹. -1 After 500 cycles, the capacity is 84.8 mAh g. -1 The capacity retention rate was 67.5%; in comparison, the initial capacity of the LiFePO4 / PEI / Li battery in Application Example 2 was 125.7 mAh g⁻¹. -1 After 500 cycles, the remaining capacity is 57.4 mAh g. -1 The capacity retention rate was 45.7%. The initial capacity of the LiFePO4 / PEI-EDA / Li battery in Application Example 3 was 129.4 mAh g⁻¹. -1 After 500 cycles, the remaining capacity is 108.8 mAh g. -1 The capacity retention rate was 84.1%. In Application Example 3, the capacity retention rate of the battery assembled with the PEI-EDA separator was significantly higher than that of the Celgard 2500 separator in Comparative Application Example 1 and the PEI separator without ethylenediamine chemical modification in Comparative Application Example 2. This indicates that the LiFePO4 / PEI-EDA / Li battery in Application Example 3 has a higher discharge specific capacity and better cycle stability.

[0122] Figure 11 The impedance performance comparison charts of the LiFePO4 / Celgard 2500 / LiCelgard 2500 battery in Application Example 1, the LiFePO4 / PEI / Li battery in Application Example 2, and the LiFePO4 / PEI-EDA / Li battery in Application Example 3 before and after 100 cycles show that the material after the polyetherimide separator modified with ethylenediamine in Application Example 3 exhibits a lower resistance value, indicating that the polyetherimide separator modified with ethylenediamine has higher ion transport performance.

[0123] Figure 12 The graph shows the cycle performance of a lithium-ion battery assembled with lithium iron phosphate as the positive electrode at a current density of 5 C. The cycle performance of lithium-ion batteries using the Celgard 2500 separator (Comparative Application Example 1), the PEI separator (Comparative Application Example 2), and the PEI-EDA separator (Comparative Application Example 3) at a 5 C rate was compared. The initial capacity of the LiFePO4 / Celgard 2500 / Li battery in Comparative Application Example 1 was 84.5 mAh g⁻¹. -1After 800 cycles, the capacity is 70.7 mAh g. -1 The capacity retention rate was 83.7%; in comparison, the initial capacity of the LiFePO4 / PEI / Li battery in Application Example 2 was 77.7 mAh g⁻¹. -1 After 800 cycles, the remaining capacity is 46.5 mAh g. -1 The capacity retention rate was 60.0%. The initial capacity of the LiFePO4 / PEI-EDA / Li battery in Application Example 3 was 90.5 mAh g. -1 After 800 cycles, the remaining capacity is 83.5 mAh g. -1 The capacity retention rate was 92.3%. In Application Example 3, the battery assembled with the PEI-EDA separator had a significantly higher discharge capacity and capacity retention rate than the batteries assembled in Comparative Application Example 1 and Comparative Application Example 2, indicating that the LiFePO4 / PEI-EDA / Li battery has a higher discharge specific capacity and better cycle stability.

[0124] Figure 13 The graph shows the cycle performance of lithium-ion batteries assembled with lithium iron phosphate as the positive electrode at a current density of 1 C. Lithium-ion batteries were assembled according to Application Example 4, and the cycle performance of lithium-ion batteries assembled with Celgard 2500 separators, PEI, and PEI-EDA separators (corresponding to Comparative Application Example 3 and Comparative Application Example 4, respectively) at a 1 C rate was compared.

[0125] The initial capacity of the LiFePO4 / Celgard 2500 / Li battery in Comparative Application Example 3 is 113.6 mAh g. -1 After 200 cycles, the capacity is 88.1 mAh g. -1 The capacity retention rate was 77.6%; in comparison, the initial capacity of the LiFePO4 / PEI / Li battery in Application Example 4 was 109.8 mAh g⁻¹. -1 After 38 cycles, the remaining capacity was 111.3 mAh g. -1 A short circuit subsequently occurred. The initial capacity of the LiFePO4 / PEI-EDA / Li battery in Application Example 4 was 119.5 mAh g⁻¹. -1 After 200 cycles, the remaining capacity is 105.3 mAh g. -1 The capacity retention rate was 88.1%. The discharge capacity and capacity retention rate of the battery assembled with the PEI-EDA separator were significantly higher than those of the Celgard 2500 separator and the PEI separator without ethylenediamine chemical modification, indicating that the LiFePO4 / PEI-EDA / Li battery in Example 4 has a higher discharge specific capacity and better cycle stability.

[0126] Figure 14The graph shows the rate performance of lithium-ion batteries assembled with lithium iron phosphate as the positive electrode. The rate performance of the LiFePO4 / Celgard 2500 / Li battery in Application Example 3, the LiFePO4 / PEI / Li battery in Comparative Application Example 1, and the LiFePO4 / PEI-EDA / Li battery in Comparative Application Example 2 were tested. The specific capacities of the LiFePO4 / Celgard 2500 / Li battery in Comparative Application Example 2 at rates of 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 C were 145.7, 142.5, 134.5, 124.0, 109.2, 98.7, 90.6, and 84.0 mAh g, respectively. -1 The specific capacities of the LiFePO4 / PEI / Li battery in Comparative Application Example 1 at rates of 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 C are 145.4, 143.3, 134.0, 121.7, 103.5, 92.6, 83.2, and 74.3 mAh g, respectively. -1 The specific capacities of the LiFePO4 / PEI-EDA / Li battery in Application Example 3 at rates of 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 C were 149.6, 146.5, 138.7, 128.8, 114.5, 104.6, 97.1, and 91.0 mAh g, respectively. -1 The specific capacity of the battery assembled with PEI-EDA separator is higher than that of the battery assembled with Celgard 2500 separator and PEI separator at all rates.

[0127] Figure 15 The graph shows the cycle performance of the lithium-ion battery assembled with lithium cobalt oxide as the positive electrode. The lithium-ion battery was assembled according to Application Example 5, and the cycle performance at 1 C rate was compared between the Celgard 2500 separator of Comparative Application Example 5, the PEI separator of Comparative Application Example 6, and the PEI-EDA lithium-ion battery of Application Example 5. The initial capacity of the LiFePO4 / Celgard 2500 / Li battery of Comparative Application Example 5 was 155.1 mAh g⁻¹. -1 After 150 cycles, the capacity is 118.0 mAh g. -1 The capacity retention rate was 76.1%. In comparison, the initial capacity of the LiFePO4 / PEI / Li battery in Application Example 6 was 143.2 mAh g⁻¹. -1 After 150 cycles, the remaining capacity is 113.2 mAh g. -1 The capacity retention rate was 79.1%. The initial capacity of the LiFePO4 / PEI-EDA / Li battery in Application Example 5 was 155.2 mAh g⁻¹. -1After 150 cycles, the remaining capacity is 138.1 mAh g. -1 The capacity retention rate was 89.0%. The cycle stability and capacity retention rate of the battery assembled with PEI-EDA separator were significantly higher than those of the PEI separator without ethylenediamine chemical modification and the Celgard 2500 separator, indicating that the LiCoO2 / PEI-EDA / Li battery has better cycle stability.

[0128] Figure 16 The graph shows the cycle performance of a lithium-ion battery assembled with lithium iron phosphate as the positive electrode at a high temperature of 60°C. The lithium-ion battery was assembled according to Application Example 6, and the cycle performance at 1 C rate was compared between the Celgard 2500 separator of Comparative Application Example 7, the PEI separator of Comparative Application Example 8, and the PEI-EDA lithium-ion battery of Application Example 6. The initial capacity of the LiFePO4 / Celgard 2500 / Li battery in Comparative Application Example 7 was 144.0 mAh g⁻¹. -1 After 100 cycles, the remaining capacity is 134.0 mAh g. -1 The capacity retention rate was 93.1%. In comparison, the initial capacity of the LiFePO4 / PEI / Li battery in Application Example 8 was 144.0 mAh g⁻¹. -1 After 6 cycles, the capacity was 137 mAh g. -1 Subsequently, the battery short-circuited and could not be charged or discharged normally. The initial capacity of the LiFePO4 / PEI-EDA / Li battery in Application Example 6 was 149.5 mAh g⁻¹. -1 After 100 cycles, the remaining capacity is 147.4 mAh g. -1 The capacity retention rate was 98.6%. The cycle stability and capacity retention rate of the battery assembled with the PEI-EDA separator were significantly higher than those of the unmodified polyetherimide separator and the Celgard 2500 separator, indicating that the LiFePO4 / PEI-EDA / Li battery has better high-temperature cycle stability.

[0129] Figure 17 The graph shows the cycle performance of a magnesium-ion battery assembled with CuFeSe2 as the positive electrode at 25°C. The PEI-EDA separator was assembled into a magnesium-ion battery according to the steps in Application Example 7, with an active material (CuFeSe2, hereinafter the same) loading of 0.9-1.1 mg. The amount of liquid electrolyte added was 120 μL. The cycle performance of the PEI-EDA separator in the magnesium-ion battery at 0.05 A g was tested. -1 Cycling performance under current. The results show that the PEI-EDA separator can be applied to magnesium-ion battery systems.

[0130] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for the preparation of a polyetherimide membrane chemically modified with a fatty diamine, characterized in that, It comprises the following steps: (1) dissolving polyetherimide and pore-forming agent in organic solvent to form casting solution, solidifying the casting solution into film by phase inversion method, and then drying to obtain polyetherimide film; (2) immersing the polyetherimide film of step (1) in a fatty diamine solution, and then drying to obtain a fatty diamine chemically modified polyetherimide separator; the polyetherimide separator is used in lithium ion batteries or magnesium ion batteries; In step (1), the phase inversion method is to coat the casting solution into film, then place it in saturated water vapor for 10-15 s, then immerse it in deionized water to solidify and remove the pore-forming agent; In step (1), the pore-forming agent is polyvinylpyrrolidone or polyethylene glycol, and the molecular weight of the pore-forming agent is 1-15 million; the organic solvent is N,N-dimethylacetamide, N,N-dimethylformamide or N-methylpyrrolidone; In step (1), the concentration of polyetherimide in the casting solution is 15-16 wt%; the concentration of pore-forming agent in the casting solution is 8-12 wt%; In step (2), the fatty diamine is ethylenediamine, propylenediamine, butylenediamine, pentanediamine or hexanediamine; the concentration of fatty diamine in the solution is 4-8 wt%; the immersion time of polyetherimide in the fatty diamine solution is 6-10 h; the solvent of the fatty diamine solution is methanol, N-methylpyrrolidone or ethanol.

2. The chemically modified polyetherimide membrane of a fatty diamine prepared according to the method of claim 1, characterized by: The fatty diamine chemically modified polyetherimide has a structural unit represented by general formula (I):

3. The fatty diamine chemically modified polyetherimide membrane of claim 2, wherein: The thickness of the fatty diamine chemically modified polyetherimide separator is 30-60 μm.

4. The application of the fatty diamine chemically modified polyetherimide separator of claim 2 in lithium ion batteries.

5. The application of the fatty diamine chemically modified polyetherimide separator of claim 2 in magnesium ion batteries.

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