A PAN-based gel modified by cretone acid and its preparation method and gel electrolyte

Abstract

The present invention provides a PAN-based gel modified by ketoacid and a preparation method thereof, including a step of preparing a ketoacid-malononitrile complex, a step of preparing a modified polyacrylonitrile, and a step of preparing a PAN-based gel modified by ketoacid. The present invention introduces an enol structure and an amine group by grafting a ketoacid-malononitrile complex based on ketoacid-modified PAN-based gel, thereby improving the solubility of the electrolyte, and also enabling the modified PAN-based gel electrolyte to coordinate with lithium ions, thereby improving the conductivity of the PAN-based gel electrolyte modified by ketoacid, thereby improving the overall conductivity of the lithium-ion battery and reducing the internal resistance. At the same time, since a cross-linking reaction can also occur between the side chains grafted with polyacrylonitrile, the mechanical strength of the gel electrolyte can be improved, the gel can be fixed and formed, and the gel can be prevented from breaking during the subsequent packaging process. The present invention also provides a gel electrolyte.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, in particular to the technical field of lithium ion battery electrolytes, and more particularly to a PAN-based gel modified with croscarmellose and a preparation method thereof, and also to an electrolyte using the PAN-based gel modified with croscarmellose. Background Art

[0002] Lithium-ion batteries are widely used as the main power source for mobile phones, tablet computers, laptops and other portable electronic products due to their relatively high energy density and relatively long cycle life. They are also gradually being used as the power source for hybrid vehicles, electric vehicles and electric non-motor vehicles. Lithium-ion batteries are mainly composed of a positive electrode, a negative electrode, a separator and an electrolyte. When the battery is connected through an external circuit, due to the different lithium chemical potentials of the positive and negative electrodes, chemical reactions take place on the electrodes, accompanied by the transfer of lithium ions inside the battery, while electrons form a current through the external circuit.

[0003] Lithium-ion batteries are composed of five parts: battery casing, positive electrode, separator, negative electrode and electrolyte. The electrolyte is one of the key materials for preparing lithium-ion batteries with high power density, high energy density, long cycle life and good safety performance. The electrolyte used to prepare lithium-ion batteries generally needs to meet the following requirements: (1) Good ionic conductivity. The electrolyte must have good ionic conductivity but not electronic conductivity. (2) High lithium ion migration number. A high lithium ion migration number can reduce the concentration polarization during the electrochemical reaction of the battery during the charging and discharging process, so that the battery maintains high energy density and power density. (3) Good stability. The electrolyte is generally present between the two electrodes. When the electrolyte is in direct contact with the electrode, it cannot react with the electrode to weaken the amount and performance of the electrolyte. (4) High mechanical strength. The electrolyte must have a high enough mechanical strength to meet the requirements of large-scale production and packaging.

[0004] From the perspective of phase state, current lithium-ion battery electrolytes can be divided into liquid electrolytes, solid electrolytes and semi-solid (gel) electrolytes. Gel polymer electrolytes (GPE) are semi-solid electrolytes mixed with liquid and solid, and the polymer molecules present a cross-linked spatial network structure. Gel polymer electrolytes reduce production safety issues such as electrode corrosion and oxidation combustion caused by leakage of organic liquid electrolytes. Compared with liquid electrolytes, gel electrolytes have many advantages: good safety, no explosion in abnormal use such as overcharge, overdischarge, impact, crushing and puncture, etc., and various shapes of batteries, flexible batteries and thin film batteries can be prepared by using soft-packed aluminum-plastic composite film shells. They contain or contain very little liquid components, and have lower reactivity than liquid electrolytes, which is more favorable for carbon electrodes as negative electrodes. Gel electrolytes can also be used as diaphragms, which can save conventional diaphragms, thereby bonding the positive and negative electrodes together, and the electrodes have good contact, which can simplify the battery structure, improve packaging efficiency, thereby improving energy and power density, and saving costs. Common gel electrolytes include polyacrylonitrile (PAN), which has excellent thermal stability and mechanical properties, as well as good film-forming properties and electrochemical windows, which are basically close to the use requirements of batteries. However, the PAN molecular chain does not contain oxygen atoms and cannot coordinate with lithium ions, so its ionic conductivity is poor when used as a gel electrolyte. Summary of the invention

[0005] In view of this, the present invention provides a PAN-based gel modified with croscarmellose and a preparation method thereof. The present invention also provides a battery comprising the PAN-based gel modified with croscarmellose to solve the problem of poor conductivity of existing PAN gel electrolytes.

[0006] In a first aspect, the present invention provides a method for preparing a PAN-based gel modified by cresol acid, comprising the following steps:

[0007] Preparation of a crotonic acid-malononitrile complex: providing crotonic acid and malononitrile, dissolving the crotonic acid in an alkaline solution and stirring until an orange-yellow solid is precipitated, adding malononitrile to the alkaline solution, continuing to stir until the solution becomes a dark purple viscous state, filtering to obtain dark blue crystals, dissolving the dark blue crystals again in an acidic solution and stirring until a yellow solid is precipitated, filtering and recrystallizing to obtain a crotonic acid-malononitrile complex;

[0008] Preparation of modified polyacrylonitrile: providing polyacrylonitrile, a hydroxylamine compound and a first polar organic solvent, dissolving the hydroxylamine compound in the first polar organic solvent and adjusting the pH to 4 to 7, then adding polyacrylonitrile to the first polar organic solvent, stirring and refluxing at 85 to 110° C. for 1 to 5 hours, filtering and washing to obtain modified polyacrylonitrile;

[0009] Preparation of PAN-based gel modified by crotonate: providing crotonate-malononitrile complex, modified polyacrylonitrile, dispersant and second polar organic solvent, dissolving the modified polyacrylonitrile and dispersant in the second polar organic solvent, adding the crotonate-malononitrile complex to the second polar organic solvent, stirring and refluxing at 85-110° C. for 1-5 h, filtering and washing with deionized water, and vacuum drying to obtain PAN-based gel modified by crotonate.

[0010] The preparation method of the PAN-based gel modified by ketoacid comprises the steps of preparing a ketoacid-malononitrile complex, preparing a modified polyacrylonitrile and preparing a PAN-based gel modified by ketoacid. In the step of preparing the ketoacid-malononitrile complex, the malononitrile is complexed to the ketoacid ring by stirring reaction to generate the ketoacid-malononitrile complex. In the step of preparing the modified polyacrylonitrile, a large number of amine groups are generated on the modified polyacrylonitrile chain by the oximation reaction of the amine group and the cyano group, and a large number of active hydroxyl groups are also introduced because the amine compound contains hydroxyl groups. In the step of preparing the PAN-based gel modified by ketoacid, the amine groups or hydroxyl groups on the double bonds of the ketoacid-malononitrile complex are activated and then undergo a cross-linking reaction with the hydroxyl groups on the modified polyacrylonitrile. The cross-linked ketoacid contains a large number of oxygen atoms and quinone structures, which can be coordinated with lithium ions, thereby greatly improving the ionic conductivity of the gel electrolyte, improving the overall conductivity of the battery, and reducing the internal resistance of the battery. In addition, since polyacrylonitrile is cross-linked through grafted side chains, it can also improve the mechanical strength of the gel electrolyte, promote gel fixation and molding, and prevent gel breakage during subsequent packaging.

[0011] Preferably, in the step of preparing the keto acid-malononitrile complex, the mass ratio of the keto acid to malononitrile is 100:25-75, the alkaline solution is at least one of a NaOH solution and a KOH solution, and the concentration of the alkaline solution is 1-10 mol / L. Both the NaOH solution and the KOH solution are strong base solutions, and the addition of the strong base solution can ionize the hydroxyl groups on the double bonds of the keto acid, thereby effectively protecting the hydroxyl groups on the double bonds of the keto acid and preventing the hydroxyl groups on the double bonds from directly complexing with malononitrile. By adjusting the mass ratio of the keto acid to malononitrile, it is ensured that malononitrile and the keto acid are fully complexed.

[0012] Preferably, in the step of preparing the crotonic acid-malononitrile complex, after adding the malononitrile, the alkaline solution is transferred to a water bath at 75 to 95° C. and stirred for 30 to 200 min;

[0013] The acidic solution is a hydrochloric acid solution or a sulfuric acid solution. After adding malononitrile, the alkaline solution is transferred to a water bath at 75-95°C and stirred for reaction, which can promote the complexation of malononitrile with the carbonyl group of crotonic acid and the generation of a new carbon-carbon double bond. The hydrochloric acid solution or the sulfuric acid solution is a stable strong acid solution. After the complexation of crotonic acid and malononitrile, they are dissolved in the acidic solution, so that the hydroxyl group on the double bond of crotonic acid is restored to obtain an acidic crotonic acid-malononitrile complex, which can also promote the hydrolysis of unreacted malononitrile, and then remove it through the subsequent recrystallization step.

[0014] Preferably, in the step of preparing the ketoic acid-malononitrile complex, the recrystallization step is: dissolving the yellow solid collected after suction filtration in deionized water again, adding acetone dropwise to the deionized water and stirring until a large amount of turbidity appears in the deionized water, and then suction filtration to collect the precipitate. The recrystallization step can purify the ketoic acid-malononitrile complex and remove unreacted malononitrile to prevent interference with subsequent cross-linking reactions.

[0015] Preferably, in the step of preparing modified polyacrylonitrile, the amine compound is at least one of hydroxylamine hydrochloride, hydroxylamine nitrate, isopropanolamine and ethanolamine, and the first polar organic solvent is at least one of water, methanol, ethanol, DMSO and DMF. Since the amine compounds all contain hydroxylamine groups (-NH2OH), a large number of amine groups and hydroxyl groups are introduced into the modified polyacrylonitrile chain, which is conducive to the cross-linking of the crotonic acid-malononitrile complex with the modified polyacrylonitrile, and further introduces enol functional groups and amine groups into the modified polyacrylonitrile, so that the prepared crotonic acid-modified PAN-based gel can coordinate with lithium ions.

[0016] Preferably, in the step of preparing modified polyacrylonitrile, the mass ratio of the polyacrylonitrile to the hydroxylamine compound is 100:1-10, the molecular weight of the polyacrylonitrile is 10-60 kD, and the step of adjusting pH is: adding a dilute acid solution or a dilute alkali solution to the polar organic solvent. Reasonable preparation of the ratio of polyacrylonitrile to the hydroxylamine compound and the molecular weight of polyacrylonitrile can effectively improve the grafting rate of polyacrylonitrile, which is beneficial to the preparation of PAN-based gel modified by keto acid in the later stage.

[0017] Preferably, in the step of preparing the PAN-based gel modified by keto acid, the mass ratio of the keto acid-malononitrile complex, modified polyacrylonitrile and dispersant is 6-30:100:1-4, and the dispersant is sodium alkyl sulfonate, stearate or oleate. By rationally preparing the ratio of the keto acid-malononitrile complex and modified polyacrylonitrile, the grafting rate of the modified polyacrylonitrile can be increased, and the uniform distribution of the amino group and the hydroxyl group on the polyacrylonitrile chain can be promoted. By adding a reasonable amount of dispersant, the keto acid-malononitrile complex and the modified polyacrylonitrile can be quickly mixed, accelerating the progress of the reaction.

[0018] Preferably, in the step of preparing the PAN-based gel modified by croton acid, the second polar organic solvent is methanol, ethanol, DMSO or DMF, and the vacuum drying condition is: drying at 40-75°C for 8-24 hours. By adding the croton acid-malononitrile complex and modified polyacrylonitrile to the second dispersant to quickly mix the two reaction substrates, conditions are provided for the grafting reaction or cross-linking reaction, thereby improving the conductivity of the croton acid-modified PAN-based gel electrolyte. The vacuum drying method can keep the oximation structure formed in the croton acid-modified PAN-based gel stable, which is beneficial to the later complexation of lithium ions.

[0019] In a second aspect, the present invention further provides a PAN-based gel modified with croscarmellose obtained by the preparation method of the PAN-based gel modified with croscarmellose as described in the first aspect.

[0020] The second aspect of the present invention is based on the introduction of enol structure and amine group by grafting ketoacid-malononitrile complex into PAN-based gel modified by ketoacid, thereby improving the solubility of the electrolyte, and also enabling the modified PAN-based gel electrolyte to coordinate with lithium ions, thereby improving the conductivity of the ketoacid-modified PAN-based gel electrolyte, thereby improving the overall conductivity of the lithium-ion battery and reducing the internal resistance. At the same time, since cross-linking reactions can also occur between the grafted side chains of polyacrylonitrile, the mechanical strength of the gel electrolyte can be improved, the gel fixation and molding can be promoted, and the gel fracture can be prevented during the subsequent packaging process.

[0021] In a third aspect, the present invention further provides a battery, which comprises the PAN-based gel modified with crotonate according to the second aspect of the present invention.

[0022] The battery of the present invention comprises a PAN-based gel modified by croton acid, and the lithium ions are coordinated and combined by the PAN-based gel electrolyte modified by croton acid, thereby greatly improving the conductivity of lithium ions in the lithium-ion battery and reducing the overall internal resistance of the lithium-ion battery.

[0023] Advantages of the present invention will be partially set forth in the following description, and partly will be obvious from the description, or may be learned through implementation of the embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the content of the present invention, it is described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] Figure 1 The images of the PAN-based gel modified with crotonate before and after stretching are based on this application;

[0026] Figure 2 This is a graph showing the tensile strength test results of the PAN-based gel modified by croton acid and compared with polyacrylonitrile;

[0027] Figure 3 This is a rate performance diagram corresponding to a battery prepared based on PAN-based gel modified with crotonate provided in Example 6 of the present invention. DETAILED DESCRIPTION

[0028] The following is a preferred embodiment of the present invention. It should be noted that a person skilled in the art may make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention. Example 1

[0029] The following is an illustrative example of a method for preparing a PAN-based gel modified with croscarmellose and the prepared PAN-based gel modified with croscarmellose, which includes the following preparation steps.

[0030] Preparation of keto acid-malononitrile complex: 100 g keto acid and 25 g malononitrile. First, dissolve keto acid in 1000 ml of 10 mol / L NaOH alkaline solution, stir the alkaline solution until an orange-yellow solid precipitates, then add malononitrile to the alkaline solution, transfer the alkaline solution to a 75°C water bath and continue stirring until the alkaline solution becomes a dark purple viscous state, and filter to obtain dark blue crystals. After collecting the dark blue crystals, add them to 100 ml of 1 mol / L hydrochloric acid solution, continue stirring for 30 min, wait for a large amount of yellow solid to precipitate in the hydrochloric acid solution, and then filter the hydrochloric acid solution to collect the yellow solid. The collected yellow solid is dissolved in deionized water again, stirred and mixed, and then acetone is added dropwise to the deionized water and stirred until a large amount of turbidity appears in the deionized water, and then the solid is collected by suction filtration. The collected solid is recrystallized to obtain the keto acid-malononitrile complex.

[0031] Preparation steps of modified polyacrylonitrile: provide 500 g of polyacrylonitrile with a molecular weight of 10 kD, 50 g of hydroxylamine hydrochloride and 1000 ml of water. First, add hydroxylamine hydrochloride to water and stir to mix, adjust the pH of the aqueous solution to 4 by adding dilute hydrochloric acid solution and dilute ammonia water, then add polyacrylonitrile to water, transfer the mixed system of water to 85°C water bath and stir and reflux for 3 h, after the reaction is completed, filter the mixed system, wash with deionized water and place in a 50°C oven to dry for 2 h to obtain modified polyacrylonitrile.

[0032] The steps of preparing the PAN-based gel modified by ketoacid are as follows: 100 g of the modified polyacrylonitrile prepared above, 6 g of the ketoacid-malononitrile complex prepared above, 1 g of sodium alkyl sulfonate and 500 ml of methanol are provided, the modified polyacrylonitrile and the dispersant sodium alkyl sulfonate are mixed in the methanol solvent, the ketoacid-malononitrile complex is added to the methanol solvent after stirring and mixing, and the mixture is transferred to a 75°C water bath and stirred and refluxed for 4 h. After the reaction is completed, the mixed system after the reaction is filtered and the gel-like substance on the filter membrane is collected, and the mixture is repeatedly washed and filtered twice with deionized water, and the gel-like substance is transferred to a 45°C vacuum drying oven and left to stand for 4 h to obtain the PAN-based gel modified by ketoacid. Example 2

[0033] The following is an illustrative example of a method for preparing a PAN-based gel modified with croscarmellose and the prepared PAN-based gel modified with croscarmellose, which includes the following preparation steps.

[0034] Preparation of keto acid-malononitrile complex: 100 g keto acid and 30 g malononitrile. First, keto acid is dissolved in 1000 ml of 8 mol / L NaOH alkaline solution, the alkaline solution is stirred until an orange-yellow solid is precipitated, and then malononitrile is added to the alkaline solution, and stirring is continued until the alkaline solution becomes dark purple and viscous, and dark blue crystals are obtained by suction filtration. After collecting the dark blue crystals, they are added to 100 ml of 1 mol / L hydrochloric acid solution, and stirring is continued for 15 min. At this time, a large amount of yellow solid is precipitated in the hydrochloric acid solution, and the hydrochloric acid solution is suction filtered to collect the yellow solid. The collected yellow solid is dissolved in deionized water again, stirred and mixed, and then acetone is added dropwise to the deionized water and stirred until a large amount of turbidity appears in the deionized water, and then the solid is collected by suction filtration. The collected solid is recrystallized to obtain the keto acid-malononitrile complex.

[0035] Preparation steps of modified polyacrylonitrile: provide 500 g polyacrylonitrile with a molecular weight of 20 kD, 40 g isopropanolamine and 1000 ml solvent DMSO (dimethyl sulfoxide). First, add isopropanolamine to DMSO and stir to mix, adjust the pH of the solution to 5 by adding dilute hydrochloric acid solution and dilute ammonia water, then add polyacrylonitrile to the solution, transfer the mixed system to a 110°C water bath and stir and reflux for 1 h, after the reaction is completed, filter the mixed system, wash with deionized water and place in a 50°C oven to dry for 2 h to obtain modified polyacrylonitrile.

[0036] The steps of preparing the PAN-based gel modified by ketoacid are as follows: 100 g of the modified polyacrylonitrile prepared above, 12 g of the ketoacid-malononitrile complex prepared above, 2 g of magnesium stearate and 500 ml of ethanol are provided, the modified polyacrylonitrile and the dispersant magnesium stearate are mixed in the ethanol solvent, the ketoacid-malononitrile complex is added to the ethanol solvent after stirring and mixing, and the mixture is transferred to a 65°C water bath and stirred and refluxed for 5 h. After the reaction is completed, the mixed system after the reaction is filtered and the gel-like substance on the filter membrane is collected, and the mixture is repeatedly washed and filtered twice with deionized water, and the gel-like substance is transferred to a 45°C vacuum drying oven and left to stand for 4 h to obtain the PAN-based gel modified by ketoacid. Example 3

[0037] The following is an illustrative example of a method for preparing a PAN-based gel modified with croscarmellose and the prepared PAN-based gel modified with croscarmellose, which includes the following preparation steps.

[0038] Preparation of keto acid-malononitrile complex: 100 g keto acid and 40 g malononitrile. First, dissolve keto acid in 1000 ml of 6 mol / L NaOH alkaline solution, stir the alkaline solution until an orange-yellow solid precipitates, then add malononitrile to the alkaline solution, transfer the alkaline solution to an 85°C water bath and continue stirring until the alkaline solution becomes a dark purple viscous state, and filter to obtain dark blue crystals. After collecting the dark blue crystals, add them to 100 ml of 1 mol / L hydrochloric acid solution and continue stirring for 45 min. At this time, a large amount of yellow solid precipitates in the hydrochloric acid solution, and filter the hydrochloric acid solution to collect the yellow solid. The collected yellow solid is dissolved in deionized water again, stirred and mixed, and then acetone is added dropwise to the deionized water and stirred until a large amount of turbidity appears in the deionized water, and then the solid is collected by suction filtration. The collected solid is recrystallized to obtain the keto acid-malononitrile complex.

[0039] Preparation steps of modified polyacrylonitrile: 500 g of polyacrylonitrile with a molecular weight of 30 kD, 30 g of ethanolamine and 1000 ml of ethanol solvent are provided. First, ethanolamine is added to ethanol and stirred to mix well, and the pH of the ethanol solution is adjusted to 4 by dropping dilute hydrochloric acid solution and dilute ammonia water, and then polyacrylonitrile is added to the ethanol solution, and the mixed system is transferred to a 65°C water bath and stirred and refluxed for 5 h. After the reaction is completed, the mixed system is filtered, washed with deionized water, and placed in a 50°C oven for 2 h to obtain modified polyacrylonitrile.

[0040] The steps of preparing the PAN-based gel modified by ketoacid are as follows: 100 g of the modified polyacrylonitrile prepared above, 18 g of the ketoacid-malononitrile complex prepared above, 2 g of magnesium oleate and 500 ml of solvent DMSO are provided, the modified polyacrylonitrile and the dispersant magnesium oleate are mixed in the DMSO solvent, the ketoacid-malononitrile complex is added to the DMSO solvent after stirring and mixing, and the mixture is transferred to a water bath at 85°C and stirred and refluxed for 3 h. After the reaction is completed, the mixed system after the reaction is filtered and the gel-like substance on the filter membrane is collected, and the mixture is repeatedly washed and filtered twice with deionized water, and then the gel-like substance is transferred to a vacuum drying oven at 45°C and allowed to stand for 4 h to obtain the PAN-based gel modified by ketoacid. Example 4

[0041] The following is an illustrative example of a method for preparing a PAN-based gel modified with croscarmellose and the prepared PAN-based gel modified with croscarmellose, which includes the following preparation steps.

[0042] Preparation of keto acid-malononitrile complex: 100 g keto acid and 50 g malononitrile. First, dissolve keto acid in 1000 ml of 4 mol / L KOH alkaline solution, stir the alkaline solution until an orange-yellow solid precipitates, then add malononitrile to the alkaline solution, transfer the alkaline solution to an 85°C water bath and continue stirring until the alkaline solution becomes a dark purple viscous state, and filter to obtain dark blue crystals. After collecting the dark blue crystals, add them to 100 ml of 1 mol / L sulfuric acid solution and continue stirring for 120 min. At this time, a large amount of yellow solid precipitates in the hydrochloric acid solution, and filter the hydrochloric acid solution to collect the yellow solid. The collected yellow solid is dissolved in deionized water again, stirred and mixed, and then acetone is added dropwise to the deionized water and stirred until a large amount of turbidity appears in the deionized water, and then the solid is collected by suction filtration. The collected solid is recrystallized to obtain the keto acid-malononitrile complex.

[0043] Preparation steps of modified polyacrylonitrile: provide 500 g of polyacrylonitrile with a molecular weight of 40 kD, 20 g of hydroxylamine hydrochloride and 1000 ml of solvent DMSO. First, add hydroxylamine hydrochloride to DMSO and stir to mix, adjust the pH of the solution to 5 by adding dilute hydrochloric acid solution and dilute ammonia water, then add polyacrylonitrile to the DMSO solution, transfer the mixed system to a 100°C water bath and stir and reflux for 2 h, and after the reaction is completed, filter the mixed system, wash with deionized water and place in a 50°C oven to dry for 2 h to obtain modified polyacrylonitrile.

[0044] The steps of preparing the PAN-based gel modified by ketoacid are as follows: 100 g of the modified polyacrylonitrile prepared above, 18 g of the ketoacid-malononitrile complex prepared above, 3 g of sodium alkyl sulfonate and 500 ml of solvent DMSO are provided, the modified polyacrylonitrile and the dispersant sodium alkyl sulfonate are mixed in the DMSO solvent, the ketoacid-malononitrile complex is added to the DMSO solvent after stirring and mixing, and the mixture is transferred to a 105°C water bath and stirred and refluxed for 1 h. After the reaction is completed, the mixed system after the reaction is filtered and the gel-like substance on the filter membrane is collected, and the mixture is repeatedly washed and filtered twice with deionized water, and then the gel-like substance is transferred to a 45°C vacuum drying oven and left to stand for 4 h to obtain the PAN-based gel modified by ketoacid. Example 5

[0045] The following is an illustrative example of a method for preparing a PAN-based gel modified with croscarmellose and the prepared PAN-based gel modified with croscarmellose, which includes the following preparation steps.

[0046] Preparation of keto acid-malononitrile complex: 100 g keto acid and 60 g malononitrile. First, dissolve keto acid in 1000 ml of 2 mol / L KOH alkaline solution, stir the alkaline solution until an orange-yellow solid precipitates, then add malononitrile to the alkaline solution, transfer the alkaline solution to a 95°C water bath and continue stirring until the alkaline solution becomes a dark purple viscous state, and filter to obtain dark blue crystals. After collecting the dark blue crystals, add them to 100 ml of 1 mol / L sulfuric acid solution and continue stirring for 60 min. At this time, a large amount of yellow solid precipitates in the hydrochloric acid solution, and filter the hydrochloric acid solution to collect the yellow solid. The collected yellow solid is dissolved in deionized water again, stirred and mixed, and then acetone is added dropwise to the deionized water and stirred until a large amount of turbidity appears in the deionized water, and then the solid is collected by suction filtration. The collected solid is recrystallized to obtain the keto acid-malononitrile complex.

[0047] Preparation steps of modified polyacrylonitrile: provide 500 g polyacrylonitrile with a molecular weight of 50 kD, 10 g ethanolamine and 1000 ml solvent DMF (N,N-dimethylformamide). First, add ethanolamine to DMF and stir to mix, adjust the pH of the solution to 6 by adding dilute hydrochloric acid solution and dilute ammonia water dropwise, then add polyacrylonitrile to the DMF solution, transfer the mixed system to a 105°C water bath and stir and reflux for 1 h, after the reaction is completed, filter the mixed system, wash with deionized water and place in a 50°C oven to dry for 2 h to obtain modified polyacrylonitrile.

[0048] The steps of preparing the PAN-based gel modified by ketoacid are as follows: 100 g of the modified polyacrylonitrile prepared above, 24 g of the ketoacid-malononitrile complex prepared above, 3 g of magnesium stearate and 500 ml of solvent DMF are provided, the modified polyacrylonitrile and the dispersant magnesium stearate are mixed in the DMF solvent, stirred and mixed, and then the ketoacid-malononitrile complex is added to the DMF solvent, and transferred to a 110°C water bath and stirred and refluxed for 1 h. After the reaction is completed, the mixed system after the reaction is filtered and the gel-like substance on the filter membrane is collected, and the gel-like substance is repeatedly washed and filtered twice with deionized water, and then the gel-like substance is transferred to a 45°C vacuum drying oven and left to stand for 4 h to obtain the PAN-based gel modified by ketoacid. Example 6

[0049] The following is an illustrative example of a method for preparing a PAN-based gel modified with croscarmellose and the prepared PAN-based gel modified with croscarmellose, which includes the following preparation steps.

[0050] Preparation of keto acid-malononitrile complex: 100 g keto acid and 75 g malononitrile. First, dissolve keto acid in 1000 ml of 1 mol / L KOH alkaline solution, stir the alkaline solution until an orange-yellow solid precipitates, then add malononitrile to the alkaline solution, transfer the alkaline solution to a 75°C water bath and continue stirring until the alkaline solution becomes a dark purple viscous state, and filter to obtain dark blue crystals. After collecting the dark blue crystals, add them to 100 ml of 1 mol / L sulfuric acid solution and continue stirring for 90 min. At this time, a large amount of yellow solid precipitates in the hydrochloric acid solution, and filter the hydrochloric acid solution to collect the yellow solid. The collected yellow solid is dissolved in deionized water again, stirred and mixed, and then acetone is added dropwise to the deionized water and stirred until a large amount of turbidity appears in the deionized water, and then the solid is collected by suction filtration. The collected solid is recrystallized to obtain the keto acid-malononitrile complex.

[0051] Preparation steps of modified polyacrylonitrile: 500 g of polyacrylonitrile with a molecular weight of 60 kD, 5 g of hydroxylamine nitrate and 1000 ml of methanol solvent are provided. First, hydroxylamine nitrate is added to methanol and stirred to mix well, and the pH of the methanol solution is adjusted to 7 by dropping dilute hydrochloric acid solution and dilute ammonia water, and then polyacrylonitrile is added to the methanol solution, and the mixed system is transferred to a 75°C water bath and stirred and refluxed for 4 h. After the reaction is completed, the mixed system is filtered, washed with deionized water, and placed in a 50°C oven for 2 h to obtain modified polyacrylonitrile.

[0052] The steps of preparing the PAN-based gel modified by ketoacid are as follows: 100 g of the modified polyacrylonitrile prepared above, 30 g of the ketoacid-malononitrile complex prepared above, 4 g of magnesium oleate and 500 ml of solvent DMF are provided, the modified polyacrylonitrile and the dispersant magnesium oleate are mixed in the DMF solvent, the ketoacid-malononitrile complex is added to the DMF solvent after stirring and mixing, and the mixture is transferred to a 95°C water bath and stirred and refluxed for 2 h. After the reaction is completed, the mixed system after the reaction is filtered and the gel-like substance on the filter membrane is collected, and the mixture is repeatedly washed and filtered twice with deionized water, and then the gel-like substance is transferred to a 45°C vacuum drying oven and left to stand for 4 h to obtain the PAN-based gel modified by ketoacid.

[0053] Comparative Example 1: Ordinary PAN gel electrolyte, that is, polyacrylonitrile gel electrolyte that has not been modified.

[0054] The difference between Comparative Example 2 and Example 1 is that the step of preparing modified polyacrylonitrile is omitted, that is, in the step of preparing the PAN-based gel modified by ketoacid, unmodified polyacrylonitrile and dispersant sodium alkyl sulfonate are mixed in methanol solvent, stirred and mixed, and then the ketoacid-malononitrile complex is added to the methanol solvent, and transferred to a 75°C water bath and stirred and refluxed for 4 hours. After the reaction is completed, the mixed system after the reaction is filtered and the gel-like substance on the filter membrane is collected, and the washing and filtration are repeated twice with deionized water, and then the gel-like substance is transferred to a 45°C vacuum drying oven and left to stand for 4 hours to obtain a PAN-based gel modified by ketoacid.

[0055] Effect Example 1: Mechanical Properties Test

[0056] like Figure 1 As shown in the figure, the schematic diagram of the PAN-based gel modified by croton acid prepared in Example 6 before and after direct stretching. Before stretching, the PAN-based gel modified by croton acid was poured into a tape-shaped mold and molded into a tape-shaped mold with a length of 4 cm and a width of 1 cm. The two ends of the tape-shaped PAN-based gel modified by croton acid were clamped by tweezers and stretched. Figure 1 As shown, the PAN-based gel modified with crotonate prepared in Example 6 will not break after being stretched by more than 250%, and has good mechanical properties.

[0057] According to GB / T 15788 "Geosynthetics Wide Strip Tensile Test Method", the tensile properties of the PAN tapes before and after modification in Comparative Examples 1-2 and Examples 1-6 were measured using a Wance TSE105D TestStar microcomputer-controlled electronic universal testing machine. A preload of 1% of the expected maximum load was applied to determine the starting point of the initial elongation test, and the load was continued to be applied until the sample broke. The test results are shown in Table 1.

[0058] Table 1 Tensile strength of PAN in various examples

[0059] Example Tensile strength (MPa) Example 1 3.12 Example 2 3.09 Example 3 3.18 Example 4 3.22 Example 5 3.15 Example 6 3.06 Comparative Example 1 1.03 Comparative Example 2 1.68

[0060] According to the test results, the tensile strength of common polyacrylonitrile without modification is very low, only 1.03 MPa. After the unmodified polyacrylonitrile in Comparative Example 2 reacts with the keto acid-malononitrile complex, the tensile strength of polyacrylonitrile is slightly improved, which may be partially cross-linked with the keto acid-malononitrile complex to improve the mechanical strength of polyacrylonitrile. Compared with the polyacrylonitrile in Comparative Examples 1 and 2, the tensile strength of the modified polyacrylonitrile prepared in Examples 1-6 is greatly improved. Due to the reaction of modified polyacrylonitrile with hydroxylamine compounds, active hydroxyl groups and amino groups are formed on the modified polyacrylonitrile chain, which is convenient for the subsequent preparation of cross-linking reaction with the keto acid-malononitrile complex in the keto acid-modified PAN-based gel step, a large amount of cross-linked polyacrylonitrile is produced, and the tensile strength of polyacrylonitrile is improved.

[0061] The continuous data obtained by tensile properties of the PAN tape corresponding to Comparative Example 1 and Example 6 are plotted, as shown in FIG. Figure 2 As shown, the PAN-based gel modified by ketoacid prepared in Example 6 will not break after being stretched by more than 900%, and the tensile strength is 3.06 MPa. The unmodified polyacrylonitrile in Comparative Example 1 breaks after being stretched by more than 500%, and the tensile strength is 1.03 MPa. The above results show that the mechanical properties of polyacrylonitrile are improved after modification, which may be related to the cross-linking reaction between polyacrylonitrile and ketoacid-malononitrile complex.

[0062] Effect Example 2: Conductivity Test

[0063] The polyacrylonitrile gel, PC (propylene carbonate) and LiPF6 in Examples 1-6 and Comparative Examples 1-2 were ultrasonically mixed in a mass ratio of 2:2:1 and then coagulated to form a gel electrolyte. The conductivity of the gel electrolyte was measured using a DDS-11A four-probe digital conductivity meter at a test temperature of 25°C. The measurement results are shown in Table 2.

[0064] Table 2 Conductivity of gel electrolyte

[0065] Example Conductivityσ(μs / cm) Example 1 44.985 Example 2 55.585 Example 3 68.54 Example 4 61.255 Example 5 64.52 Example 6 59.335 Comparative Example 2 18.76

[0066] As shown in Table 2, compared with the conductivity of the polyacrylonitrile gel in Comparative Example 2, the conductivity of the PAN-based gel modified with ketoacid in Examples 1-6 is increased by more than 3 times. This may be because the modified polyacrylonitrile and the ketoacid-malononitrile complex fully react to form multiple active groups, such as the enol structure hydroxyl group on the ketoacid, which is easier to coordinate with and transport lithium ions, thereby improving the conductivity of the electrolyte.

[0067] Effect Example 3: Rate Performance Test

[0068] The PAN-based gel modified with cresol prepared in Example 1 was ultrasonically mixed with PC and LiPF6 in a mass ratio of 2:2:1 and solidified to form a gel electrolyte. The gel electrolyte was applied to a graphite / metal lithium battery system, and the encapsulated battery was tested for rate performance. The battery corresponding to the electrolyte prepared in Example 1 was tested for rate performance using an electrochemical workstation. The test results are shown in FIG. Figure 3 As shown. The battery was cycled at a current density of 0.1 C for 30 cycles, 0.2 C for 10 cycles, 0.5 C for 10 cycles, 1 C for 10 cycles, 2 C for 10 cycles, and 0.5 C for 10 cycles, and finally recovered to a current density of 0.1 C for one cycle. In the 30 cycles at a current density of 0.1 C, the average specific capacity was 376.4 mAh g -1 At a current density of 0.2 C, the average specific capacity is 352.3 mAh g -1 At a current density of 0.5 C, the average specific capacity is 308.5 mAh g -1 At a current density of 1 C, the average specific capacity is 272.8 mAh g -1 At a current density of 2 C, the average specific capacity is 219.4 mAh g -1 At a current density of 0.5 C, the average specific capacity is 313.8 mAh g -1 When the current density was restored to 0.1 C, the specific capacity was restored to 369.3 mAh g -1 The above experimental results show that the lithium-ion battery prepared based on the PAN-based gel modified by ketoacid in the present invention has good rate performance, and when the current density is restored to the initial 0.1 C, its specific capacity reaches 98.1% of the initial average specific capacity, which also shows that the lithium-ion battery prepared based on the PAN-based gel modified by ketoacid in the present application has good chemical stability and cycle stability.

[0069] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a PAN-based gel modified by cresol acid, characterized in that: The following steps are involved: Preparation of a crotonic acid-malononitrile complex: providing crotonic acid and malononitrile, dissolving the crotonic acid in an alkaline solution and stirring until an orange-yellow solid is precipitated, adding malononitrile to the alkaline solution, continuing to stir until the solution becomes a dark purple viscous state, filtering to obtain dark blue crystals, dissolving the dark blue crystals again in an acidic solution and stirring until a yellow solid is precipitated, filtering and recrystallizing to obtain a crotonic acid-malononitrile complex; Preparation of modified polyacrylonitrile: providing polyacrylonitrile, a hydroxylamine compound and a first polar organic solvent, dissolving the hydroxylamine compound in the first polar organic solvent and adjusting the pH to 4 to 7, then adding polyacrylonitrile to the first polar organic solvent, stirring and refluxing at 85 to 110° C. for 1 to 5 hours, filtering and washing to obtain modified polyacrylonitrile; Preparation of PAN-based gel modified by crotonate: providing crotonate-malononitrile complex, modified polyacrylonitrile, dispersant and second polar organic solvent, dissolving the modified polyacrylonitrile and dispersant in the second polar organic solvent, adding the crotonate-malononitrile complex to the second polar organic solvent, stirring and refluxing at 65-110° C. for 1-5 h, filtering and washing with deionized water, and vacuum drying to obtain PAN-based gel modified by crotonate.

2. The method for preparing PAN-based gel modified by cretone acid according to claim 1, characterized in that: In the step of preparing the crotonic acid-malononitrile complex, the mass ratio of the crotonic acid to malononitrile is 100:25-75, the alkaline solution is at least one of a NaOH solution and a KOH solution, and the concentration of the alkaline solution is 1-10 mol / L.

3. The method for preparing PAN-based gel modified by cretone acid according to claim 1, characterized in that: In the step of preparing the keto acid-malononitrile complex, after adding the malononitrile, the alkaline solution is transferred to a water bath at 75 to 95° C. and stirred for 30 to 200 minutes; The acidic solution is a hydrochloric acid solution or a sulfuric acid solution.

4. The method for preparing PAN-based gel modified by cretone acid according to claim 1, characterized in that: In the step of preparing the crotonic acid-malononitrile complex, the recrystallization step is: dissolving the yellow solid collected after suction filtration in deionized water again, adding acetone dropwise into the deionized water and stirring until a large amount of turbidity appears in the deionized water, and then collecting the precipitate by suction filtration.

5. The method for preparing PAN-based gel modified by cretone acid according to claim 1, characterized in that: In the step of preparing modified polyacrylonitrile, the amine compound is at least one of hydroxylamine hydrochloride, hydroxylamine nitrate, isopropanolamine and ethanolamine, and the first polar organic solvent is at least one of water, methanol, ethanol, DMSO and DMF.

6. The method for preparing PAN-based gel modified by cretone acid according to claim 1, characterized in that: In the step of preparing modified polyacrylonitrile, the mass ratio of the polyacrylonitrile to the hydroxylamine compound is 100:1-10, the molecular weight of the polyacrylonitrile is 10-60 kD, and the step of adjusting pH is: adding a dilute acid solution or a dilute alkali solution dropwise to the polar organic solvent.

7. The method for preparing PAN-based gel modified by cretone acid according to claim 1, characterized in that: In the step of preparing the PAN-based gel modified by crotonic acid, the mass ratio of the crotonic acid-malononitrile complex, modified polyacrylonitrile and dispersant is 6-30:100:1-4, and the dispersant is sodium alkyl sulfonate, stearate or oleate.

8. The method for preparing PAN-based gel modified by cretone acid according to claim 1, characterized in that: In the step of preparing the PAN-based gel modified by crotonic acid, the second polar organic solvent is methanol, ethanol, DMSO or DMF, and the vacuum drying condition is: drying at 40-75° C. for 8-24 h.

9. A PAN-based gel modified with croscarmellose obtained by the method for preparing a PAN-based gel modified with croscarmellose as claimed in any one of claims 1 to 8.

10. A gel electrolyte, characterized in that: The invention comprises the PAN-based gel modified with croton acid as claimed in claim 9.

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