CN115249870A - Modification method of alginate fibers and application of alginate fibers in lithium ion battery diaphragm - Google Patents

Abstract

The invention belongs to the field of lithium ion batteries, and particularly relates to a modification method of alginate fibers and application of the alginate fibers in a lithium ion battery diaphragm. The biomass battery diaphragm with a 3D structure, which is commonly used in liquid lithium ion batteries and solid polymer lithium ion batteries, is successfully prepared by adopting alginate fibers, sodium periodate, hydrochloric acid and polyether amine as raw materials. The material has excellent appearance, retains the 3D structure of alginate fibers, provides a channel for the rapid transmission and transfer of lithium ions, and has good mechanical strength and good electrochemical performance. The solid-state battery and the liquid-state battery respectively form an LFP half battery test, the specific capacity can reach 130mAh/g/140mAh/g when 2C (1C = 170mAhg-1) is circulated, and the capacity retention rate is stabilized to be more than 95% after 100 cycles of circulation. The diaphragm has good wettability, thermal stability and mechanical property, the preparation process is simple, the material price is low, the preparation environment has no special requirement, and a new method is provided for preparing the lithium ion Chi Guye general diaphragm.

Description

Modification method of alginate fibers and application of alginate fibers in lithium ion battery diaphragm

Technical Field

The invention belongs to the field of metal batteries, and particularly relates to a modification method of alginate fibers and application of the alginate fibers in a lithium ion battery diaphragm.

Background

A series of environmental problems caused by the use of fossil energy are gradually being emphasized. At the present stage, there is an urgent need to solve the problems of energy storage and conversion, making renewable energy sources to reduce the dependence on traditional (non-renewable) energy sources. Among the numerous energy storage technologies, lithium batteries play an important role. However, the traditional lithium battery diaphragm (such as a PP diaphragm) is processed from petrochemical products, cannot be regenerated and is difficult to be applied to a liquid lithium ion battery and a solid lithium ion battery at the same time, and along with the needs of life and production, the current commonly used diaphragm is difficult to support the circulation of the battery under high rate, and has poor mechanical strength, high temperature intolerance and other problems, which bring potential safety hazards, so that a high-performance lithium ion battery diaphragm which is green, environment-friendly and general in solid-liquid is urgently needed to replace the existing diaphragm.

The alginate fiber as a degradable natural biological polysaccharide has low cost and is environment-friendly, and has good mechanical property and excellent plasticity. The presence of ligand ions (Ca 2+, H +) in the alginate fibers makes the alginate fibers have good flame retardancy and thermal stability. The alginate fiber contains a large amount of-OH and-COOH, and the electrochemical performance of the alginate fiber can be more excellent through simple chemical modification. Polyetheramines are commonly used as plasticizers, have reactive terminal amine groups, and can react with the epoxy groups on the oxidized alginate fibers.

The alginate fiber can be simply processed into the diaphragm with controllable thickness and appearance, and can be applied to the lithium ion battery through modification processing

Disclosure of Invention

The invention designs a solid-liquid universal lithium ion battery diaphragm of polyether amine grafted alginate fibers by using natural and environment-friendly renewable alginate fibers as a base material.

The polyether amine is used as a common plasticizer, has two active terminal amine groups, is commonly used for improving the material strength or constructing a cross-linked network, and currently, the research on the electrochemical performance optimization of the polyether amine on natural biological polysaccharide fibers is less. Because the activity of the polyether amine has an active end group, the polyether amine can be grafted with the modified alginate fiber after selective oxidation, and simultaneously, the appearance of the alginate fiber diaphragm can be controlled by controlling the grafting of polyether amine with different molecular weights, and pores with uniform distribution can be constructed by selecting a proper grafting ratio. Because the natural alginate fibers contain a large amount of-COOH, the grafted polyether amine has more-O-bonds and C = N bonds, and can be used as an active site for lithium ion transmission, thereby being beneficial to the lithium ion transmission between an electrolyte and a diaphragm and greatly improving the multiplying power and the cycle performance of a lithium battery. In the aspect of solid polymer batteries, the diaphragm can be used as a framework material to increase the mechanical strength of polymer electrolyte, so that the problem of low strength of the polymer after being directly combined with a plasticizer is avoided, the structure of the diaphragm is far superior to that of a pure PEO electrolyte in the aspect of dendritic crystal inhibition, and the polyether amine and the PEO have similar structures, so that the fusion of the PEO and the modified alginate fiber framework can be better promoted, a cross-linked network is formed, the resistance of the electrolyte is reduced, and the 3D structure also effectively solves the problem of irreversible Li + transmission path of the solid electrolyte of the polymer. Therefore, the separator for liquid lithium batteries and PEO-based solid lithium batteries has good performance and great practical potential.

The preparation method disclosed by the invention is simple in preparation process, does not need expensive equipment, is excellent in performance of the obtained product, is environment-friendly, and has wide prospects in the application of liquid lithium ion batteries and solid polymer lithium ion batteries.

A modification method of alginate fibers specifically comprises the following steps:

a modification method of alginate fibers comprises the following steps:

1) Adding Alginate Fiber (AF) into HCl solution, standing for 1-4 hours at room temperature, and washing with water to obtain acidified alginate fiber;

2) Placing the product of the step 1) in deionized water at room temperature, adding sodium periodate aqueous solution into the deionized water, reacting for 12 to 24 hours in a dark place, and then washing the mixture with ethanol to obtain oxidized alginate fibers;

3) Putting the product of the step 2) in an organic solvent, adding polyetheramine into the organic solvent at room temperature for reaction, and then cleaning and drying the product (preferably drying the product at 80 ℃) to obtain polyetheramine grafted alginate fibers;

the dosage ratio of the alginate fiber to the sodium periodate is (1-10) g:0.1mmol; preferably 2g:0.1mmol;

the mass ratio of the alginate fibers to the polyether amine is 5-20:1, preferably 10:1.

further, the HCl solution is preferably 1M HCl solution; the concentration of the sodium periodate aqueous solution is 1M; the organic solvent is absolute ethyl alcohol.

Further, the molecular weight of the polyetheramine is 230 to 2000 (preferably 230, 400 or 2000, most preferably 400).

The invention also provides application of the polyether amine grafted alginate fiber prepared by the modification method in a lithium battery liquid diaphragm or a lithium battery solid diaphragm.

Furthermore, when the polyether amine grafted alginate fiber prepared by the modification method is applied to a lithium battery liquid diaphragm, the polyether amine grafted alginate fiber is directly cut into pieces according to the required size and then is put into lithium battery assembly to be used as the diaphragm.

Further, when the polyether amine grafted alginate fiber prepared by the modification method is applied to a solid diaphragm of a lithium battery, the application comprises the following steps:

uniformly pouring a prepared mixed solution of polyethylene oxide (PEO) and lithium bistrifluoromethylsulfonyl imide (LiTFSI) on polyether amine grafted alginate fibers, air-drying and shaping at room temperature, and drying moisture in vacuum to obtain the lithium ion battery polymer solid electrolyte with the modified alginate fibers as a framework.

Further, the mass ratio of the PEO to the LiTFSI is 5:1, the solvent used in the preparation is anhydrous acetonitrile, and PEO and LiTFSI are fully stirred in the solvent to be uniformly mixed to obtain the required mixed solution.

Further, the vacuum drying is vacuum drying at 65 ℃ for 24 hours.

Further, the room temperature air-drying and shaping is to stand for 12 hours at room temperature.

Compared with the prior art, the invention has the following advantages:

the main material of the invention is alginate fiber which is taken from brown algae, is an environment-friendly renewable biological polysaccharide material and is environment-friendly, and the alginate fiber which is a natural high-temperature resistant flame retardant material can adapt to the working environment at high temperature and can avoid the risk of ignition of the lithium ion battery at high temperature to a certain extent. Based on the excellent performance of the alginate fibers, the diaphragm prepared by the method has good wettability, thermal stability and mechanical performance, the diaphragm has the premise of stable operation at a higher temperature due to the excellent thermal stability of the alginate fibers, and the diaphragm can inhibit the generation of lithium dendrites to a certain degree while having flexibility due to the good mechanical performance. The solid-state battery and the liquid-state battery respectively form an LFP half battery test, the specific capacity can reach 130mAh/g and 140mAh/g by 2C (1C = 170mAhg-1) circulation, and the capacity retention rate is stabilized to be more than 95% after 100 cycles of circulation.

The lithium ion battery diaphragm prepared by the invention has better cycle capacity performance and rate capability in a liquid lithium ion battery, and is far superior to the current commercial PP diaphragm. The diaphragm prepared by the invention has higher mechanical strength, can effectively inhibit the generation of lithium dendrites in the long-time charge-discharge cycle process, and prolongs the effective working time of the battery.

The lithium ion battery diaphragm prepared by the invention can form a solid polymer electrolyte with a cross-linked network with PEO, and can be used as a framework material of the polymer electrolyte, because the plasticizer is directly contacted with the PEO, the mechanical strength of the PEO is reduced, the tensile strength of the PEO is poorer, and the tensile strength is greatly improved after the framework is added. The mechanical strength is provided on the premise of ensuring flexibility, the battery can work stably for a long time, the short circuit is effectively avoided, and the polymer electrolyte can be adapted to a high-voltage electrode (the LSV is higher than the stability of 4.3V) due to the existence of a diaphragm framework. The 3D space structure solves the problem of irreversible transformation in the lithium ion transmission process, the grafted alginate fiber has a certain lithium ion transmission effect due to the increase of active sites (-O-, C = N), and the transmission capability of lithium ions is greatly improved due to the good interface compatibility of the alginate fiber.

The diaphragm provided by the invention is simple in manufacturing process, can be synthesized in a large amount, is low in material price, does not need expensive preparation cost, is environment-friendly in preparation and material selection, can be widely applied to lithium ion batteries, and provides a new method for preparing the lithium ion Chi Guye general diaphragm.

Drawings

FIG. 1 is a scanning electron microscope image of the AF-PEA400 diaphragm obtained in example 1, and the diaphragm has a 3D fiber structure and abundant pores, is uniformly distributed, and has a smooth fiber surface. Abundant pores are beneficial to increasing the channel for rapidly transmitting lithium ions, and the defect of irreversible lithium ion transmission is overcome to a certain extent.

FIG. 2 is a scanning electron micrograph of the AF-PEA2000 separator obtained in example 2, a 3D fiber structure can be observed, and the porosity is less than that of AF-PEA400 in example 1. Due to the fact that the grafted polyether amine has different molecular weights, the morphology of the fiber membrane is different, and the capacity of the membrane for transmitting lithium ions can be slightly reduced due to fewer pores.

Fig. 3 shows that the separators prepared in examples 1 to 3 and the commercial PP separator are separators, lithium iron phosphate is used as a positive electrode, a lithium plate is used as a negative electrode, lithium hexafluorophosphate electrolyte is added into the separator under argon atmosphere in a glove box to assemble LFP/AF-PEA230/Li, LFP/AF-PEA400/Li, LFP/AF-PEA2000/Li and LFP/PP/Li button cells, and the cycle performance of the four batteries under 2C (1c =170mah/g) rate is measured at room temperature by using a blue cell testing system. The capacity retention rate of the battery assembled by the diaphragm prepared in the embodiment 1-3 after 100 times of charging and discharging is higher than 99%, the coulombic efficiency is always close to 100%, the good cycling stability of the battery is proved, the specific capacity of the battery is higher than that of a commercial PP diaphragm, and the good ion transmission performance of the battery is further proved.

Fig. 4 is a charge-discharge cycle diagram of the LFP/AF-PEA400/Li battery assembled by using AF-PEA400 as a diaphragm, lithium iron phosphate as a positive electrode, a lithium plate as a negative electrode, and a lithium hexafluorophosphate electrolyte in example 1 at room temperature at a rate of 2C. After 500 cycles, the coulombic efficiency is always kept above 99%, and the lithium ion battery has excellent capacity retention rate and long-time working capacity.

Fig. 5 shows that LFP/AF-PEA230/Li, LFP/AF-PEA400/Li, LFP/AF-PEA2000/Li, and LFP/PP/Li button cells are assembled by respectively using the separators prepared in examples 1 to 3 and the commercial PP separator as separators, using lithium iron phosphate as a positive electrode, using a lithium hexafluorophosphate electrolyte as a negative electrode, and adding lithium hexafluorophosphate electrolyte under an argon atmosphere in a glove box, and the impedance performance of the assembled liquid lithium ion cells is measured at room temperature, and it can be seen that the separators AF-PEA230, AF-PEA400, and AF-PEA2000 prepared in examples 1 to 3 have superior bulk resistance and interface resistance to those of the PP separator due to their excellent 3D structure and excellent liquid absorption ability of alginate fibers, and due to the abundant-O-, C = N functional groups brought by grafting, which illustrates that the modified alginate fiber material facilitates the transmission of lithium ions in the separator and the electrochemical reaction at the interface.

FIG. 6 shows that the polymer electrolytes PEO @ AF-PEA230, PEO @ AF-PEA400, PEO @ AF-PEA2000 and pure PEO electrolyte prepared in examples 4-6 are subjected to stress strain test, and the tensile strength of the polymer solid electrolyte is greatly improved to be more than 3.8MPa due to the fact that the AF-PEA diaphragm is added as a framework, and compared with the tensile strength of 0.2MPa of the pure PEO solid electrolyte, the introduction of the framework can effectively inhibit dendritic crystals from being generated, and the cycle performance of the battery is improved.

FIG. 7 shows schematically the charge and discharge cycles of the polymer electrolytes PEO @ AF-PEA230, PEO @ AF-PEA400, PEO @ AF-PEA2000 and pure PEO electrolytes prepared in examples 4-6 under the argon atmosphere of glove box, respectively assembled with lithium iron phosphate positive electrode material and lithium sheet negative electrode material into LFP/PEO @ AF-PEA230/Li, LFP/PEO @ AF-PEA400/Li, LFP/PEO @ AF-PEA2000/Li and LFP/PEO/Li button cells, measured at 80 ℃ by using a blue cell testing system, at 2C (1C =. MAh g-1). It can be clearly observed that the batteries using the polymer electrolytes prepared in examples 4 to 6 have stable cycle, higher specific capacity and excellent capacity retention, and compared with pure PEO electrolyte, the electrolyte prepared by the method of the present invention has dendrite short-circuiting generated around 60 cycles, and the electrolyte prepared by the method of the present invention has no dendrite short-circuiting phenomenon, which indicates that the 3D skeleton electrolyte prepared in examples 4 to 6 of the present invention effectively inhibits the generation of dendrites.

FIG. 8 is a schematic view of the charge and discharge cycles of an LFP/PEO @ AF-PEA400/Li battery assembled by the PEO @ AF-PEA400 and lithium iron phosphate positive electrode material and the lithium sheet negative electrode material at 80 ℃ and 2C rate in example 4. After 1500 cycles, the coulombic efficiency is always kept above 99.5%, and the capacity per circle is attenuated by only 0.013%, so that the capacity retention rate is excellent, and the capacity of long-time work is realized.

FIG. 9 is the impedance of the polymer electrolytes prepared in examples 4-6, PEO @ AF-PEA230, PEO @ AF-PEA400, PEO @ AF-PEA2000 and PEO polymer electrolyte assembled into LFP/PEO @ AF-PEA230/Li, LFP/PEO @ AF-PEA400/Li, LFP/PEO @ AF-PEA2000/Li, LFP/PEO/Li button cells, respectively, at 80 ℃ using an electrochemical workstation. It is clearly observed that the bulk and interfacial resistance of the batteries using PEO @ AF-PEA230, PEO @ AF-PEA400, PEO @ AF-PEA2000 are less than that of the pure PEO polymer electrolyte. The excellent 3D structure of the fiber diaphragm and the existence of a large number of active functional groups (-O-, C = N) are greatly helpful for the ion transmission performance of the lithium ion battery, the lithium ion transmission rate is improved by the cross-linked network, and the polymer electrolyte prepared by the method has excellent interface performance.

FIG. 10 is a performance graph of SS/AF-PEA/Li and SS/PEO @ AF-PEA/Li button cells assembled from the diaphragm materials prepared in examples 1-6, stainless steel sheets and lithium sheets, respectively, and tested by linear sweep voltammetry using an electrochemical workstation. It can be seen that the membranes made in examples 1-6 remain stable at a voltage of 4.3V, meaning that the solid-liquid membranes can be adapted to higher voltage electrodes. Compared with pure PEO with the voltage lower than 4.0V, the solid polymer electrolyte effectively solves the problem that the solid polymer electrolyte is difficult to adapt to a high-voltage electrode, and also shows the excellent stability of the framework.

FIG. 11 is a graph of the vertical combustion performance of AF-PEA400 and PEO @ AF-PEA400 in example 4, wherein Remove indicates that the fire source is removed, no open fire is generated after the flame is ignited by the outer flame of an alcohol lamp for 4s, and the AF-PEA and the PEO @ AF-PEA400 are self-extinguished after the fire source is removed, compared with the case that the open fire is generated in a PP diaphragm and pure PEO solid electrolyte for 3s and the fire is violently combusted, the diaphragm prepared by the method has better flame retardant performance, and due to the excellent flame retardant property of the alginate fiber, the diaphragm provides a new choice for the flame retardant of lithium ion liquid and solid batteries, and the use safety is improved.

FIG. 12 is an optical photograph of AF-PEA400 and PEO @ AF-PEA400 in example 4 at different temperatures, and in the process of gradually increasing the temperature from 20 ℃ to 200 ℃, the color of the fiber diaphragm is slightly deepened along with the rise of the baking temperature, but the diaphragm is uniformly and flatly kept, and the occurrence of short circuit caused by the curling deformation of the battery diaphragm when the battery diaphragm is used at high temperature is effectively avoided.

FIG. 13 is a structural diagram for synthesizing AF-PEA400 in example 4. The preparation process of the diaphragm needs to ensure the circulation stability of the battery by pickling calcium alginate with hydrochloric acid with certain concentration, but part of Ca in the whole structure is still reserved ²⁺ Ions can ensure the mechanical strength and the flame retardant capability of the diaphragm, and the AF-PEA400 diaphragm is prepared by oxidation reaction and PEA grafting, and the structural formula is shown in the figure.

Detailed Description

The technical solution of the present invention will be described in detail with reference to specific examples.

In the following examples, the amounts of the raw materials used in the battery assembly process were the same, and the parameter settings were the same for the same test procedure.

Example 1 a method for modifying alginate fibers, comprising the steps of:

and (3) placing 3g of alginate fiber (AF, namely calcium alginate fiber) in 150 ml of 1M HCl solution, standing for reaction for 2H, taking out, and washing with deionized water to obtain acidified alginate fiber (H-AF).

Placing H-AF in 200 ml deionized water, adding 1.5 ml of 0.1M sodium periodate aqueous solution, standing in the dark for 24 hours, taking out and washing with absolute ethyl alcohol to obtain the oxidized alginate fiber (CHO-AF).

And (2) placing the CHO-AF in 100 ml of absolute ethyl alcohol, then adding 0.3g of polyetheramine D-400 into the CHO-AF, standing for 24 hours, taking out the CHO-AF, washing the CHO-AF with the absolute ethyl alcohol, carrying out suction filtration to prepare fiber paper, and drying the fiber paper at the temperature of 80 ℃ to obtain the polyetheramine grafted alginate fiber (AF-PEA 400).

And (3) cutting the final product by using a die with the diameter of 15mm to serve as a battery diaphragm, using lithium iron phosphate as a positive electrode and a lithium sheet as a negative electrode, adding LiPF6 electrolyte into a glove box to assemble the LFP/AF-PEA400/Li button battery, performing charge-discharge circulation on a blue battery test system at room temperature at the current density of 2C (1C =170mAh/g), and testing the impedance of the battery by using an electrochemical workstation at room temperature.

The SS/AF-PEA400/Li button cell was then assembled with the above material AF-PEA400 using stainless steel sheets, lithium sheets and lithium hexafluorophosphate electrolyte, and subjected to LSV testing in an electrochemical workstation.

Embodiment 2 a method for modifying alginate fibers, comprising the steps of:

and (3) placing 3g of Alginate Fiber (AF) in 150 ml of 1M HCl solution, standing for reacting for 2H, taking out, and washing with deionized water to obtain acidified alginate fiber (H-AF).

Placing H-AF in 200 ml deionized water, adding 1.5 ml of 0.1M sodium periodate aqueous solution, standing in the dark for 24 hours, taking out and washing with absolute ethyl alcohol to obtain the oxidized alginate fiber (CHO-AF).

And (2) placing the CHO-AF in 100 ml of absolute ethyl alcohol, then adding 0.3g of polyetheramine D-2000 into the CHO-AF, standing for 24 hours, taking out the CHO-AF, cleaning the CHO-AF with the absolute ethyl alcohol, carrying out suction filtration to prepare fiber paper, and drying the fiber paper at the temperature of 80 ℃ to obtain the polyetheramine grafted alginate fiber (AF-PEA 2000).

And (3) taking a die cutting piece with the diameter of 15mm as a battery diaphragm of the final product, taking lithium iron phosphate as a positive electrode and a lithium piece as a negative electrode, adding LiPF6 electrolyte into a glove box to assemble the LFP/AF-PEA2000/Li button battery, carrying out charge-discharge circulation on a blue battery test system at room temperature at the current density of 2C (1C =170mAh/g), and testing the impedance of the button battery formed according to the steps at room temperature by using an electrochemical workstation. SS/AF-PEA2000/Li button cell assembled by using stainless steel sheet, lithium sheet and lithium hexafluorophosphate electrolyte and the material AF-PEA2000 is used for LSV test at an electrochemical workstation.

Embodiment 3 a method for modifying alginate fibers, comprising the steps of:

and (3) placing 3g of Alginate Fiber (AF) in 150 ml of 1M HCl solution, standing for reacting for 2H, taking out, and washing with deionized water to obtain acidified alginate fiber (H-AF).

Placing H-AF in 200 ml deionized water, adding 1.5 ml of 0.1M sodium periodate aqueous solution, keeping away from light, standing for reaction for 24 hours, taking out, and washing with absolute ethyl alcohol to obtain oxidized alginate fiber (CHO-AF).

And (2) placing CHO-AF in 100 ml of absolute ethyl alcohol, then adding 0.3g of polyetheramine D-230 into the absolute ethyl alcohol, standing for 24 hours, taking out the mixture, cleaning the mixture by using the absolute ethyl alcohol, performing suction filtration to prepare fiber paper, and drying the fiber paper at the temperature of 80 ℃ to obtain the polyetheramine grafted alginate fiber (AF-PEA 230).

And (3) taking a die cutting piece with the diameter of 15mm as a battery diaphragm of the final product, taking lithium iron phosphate as a positive electrode and a lithium piece as a negative electrode, adding LiPF6 electrolyte into a glove box to assemble the LFP/AF-PEA230/Li button battery, carrying out charge-discharge circulation on a blue battery test system at room temperature at the current density of 2C (1C =170mAh/g), and testing the impedance of the button battery formed according to the steps at room temperature by using an electrochemical workstation.

SS/AF-PEA230/Li button cells assembled from stainless steel sheets, lithium hexafluorophosphate electrolyte and the material AF-PEA230 described above were subjected to LSV testing at the electrochemical workstation.

Example 4 a method for modifying alginate fibers, comprising the steps of:

and (3) placing 2g of Alginate Fiber (AF) in 100 ml of 1M HCl solution, standing for reacting for 2H, taking out, and washing with deionized water to obtain acidified alginate fiber (H-AF).

Placing H-AF in 200 ml deionized water, adding 1 ml of 0.1M sodium periodate aqueous solution, keeping out of the sun, standing for reaction for 24 hours, taking out, and washing with absolute ethyl alcohol to obtain oxidized alginate fiber (CHO-AF).

And (2) placing the CHO-AF in 100 ml of absolute ethyl alcohol, adding 0.2g of polyetheramine D-400 into the CHO-AF, standing for 24 hours, taking out the CHO-AF, washing the CHO-AF with the absolute ethyl alcohol, performing suction filtration to prepare fiber paper, and drying the fiber paper at the temperature of 80 ℃ to obtain the polyetheramine grafted alginate fiber (AF-PEA 400).

2g of polyethylene oxide (PEO) and 0.4 g of lithium bistrifluoromethylsulfonyl imide (LiTFSI) are dissolved in 40mL of anhydrous acetonitrile, stirred uniformly at room temperature by using a magnetic stirrer, poured on the polyetheramine grafted alginate fiber AF-PEA400, kept stand for 12 hours at room temperature for shaping, and dried in vacuum at 65 ℃ for 24 hours to prepare the PEO @ AF-PEA400 polymer electrolyte.

And (3) assembling the final product into an LFP/PEO @ AF-PEA400/Li button cell by using a die cutting piece with the diameter of 15mm as a solid electrolyte, using lithium iron phosphate as a positive electrode and a lithium sheet as a negative electrode in a glove box, performing charge-discharge circulation on a blue cell test system at the temperature of 80 ℃ at the current density of 2C (1C =170mAh/g), and testing the impedance of the button cell formed according to the steps at the temperature of 80 ℃ by using an electrochemical workstation. SS/PEO @ AF-PEA230/Li button cells assembled with the above material PEO @ AF-PEA400 using stainless steel sheets, lithium sheets were tested for LSV using an electrochemical workstation at 80 ℃.

Example 5 a method of modifying alginate fibers, comprising the steps of:

and (3) placing 2g of Alginate Fiber (AF) in 100 ml of 1M HCl solution, standing for reacting for 2H, taking out, and washing with deionized water to obtain acidified alginate fiber (H-AF).

Placing H-AF in 200 ml deionized water, adding 1 ml of 0.1M sodium periodate aqueous solution, keeping out of the sun, standing for reaction for 24 hours, taking out, and washing with absolute ethyl alcohol to obtain oxidized alginate fiber (CHO-AF).

And (2) placing the CHO-AF in 100 ml of absolute ethyl alcohol, adding 0.2g of polyetheramine D-230 into the CHO-AF, standing for 24 hours, taking out the CHO-AF, cleaning the CHO-AF with the absolute ethyl alcohol, performing suction filtration to prepare fiber paper, and drying the fiber paper at the temperature of 80 ℃ to obtain the polyetheramine grafted alginate fiber (AF-PEA 230).

Dissolving 2g of PEO and 0.4 g of LiTFSI in 40mL of anhydrous acetonitrile, uniformly stirring, pouring on AF-PEA230, standing at room temperature for 12 hours for shaping, and then drying in vacuum at 65 ℃ for 24 hours to prepare the PEO @ AF-PEA230 polymer electrolyte.

And (3) assembling the final product into an LFP/PEO @ AF-PEA230/Li button cell by using a die cutting piece with the diameter of 15mm as a solid electrolyte, using lithium iron phosphate as a positive electrode and a lithium sheet as a negative electrode in a glove box, performing charge-discharge circulation on a blue cell test system at the temperature of 80 ℃ at the current density of 2C (1C =170mAh/g), and testing the impedance of the button cell formed according to the steps by using an electrochemical workstation at the temperature of 80 ℃. SS/PEO @ AF-PEA230/Li button cells assembled from stainless steel, lithium and the above-described material PEO @ AF-PEA230 were tested for LSV using an electrochemical workstation at 80 ℃.

Example 6 a method for modifying alginate fibers, comprising the steps of:

and (3) placing 2g of Alginate Fiber (AF) in 100 ml of 1M HCl solution, standing for reacting for 2H, taking out, and washing with deionized water to obtain acidified alginate fiber (H-AF).

Placing H-AF in 200 ml deionized water, adding 1 ml of 0.1M sodium periodate aqueous solution, keeping out of the sun, standing for reaction for 24 hours, taking out, and washing with absolute ethyl alcohol to obtain oxidized alginate fiber (CHO-AF).

And (2) placing the CHO-AF in 100 ml of absolute ethyl alcohol, adding 0.2g of polyetheramine D-2000 into the CHO-AF, standing for 24 hours, taking out the CHO-AF, cleaning the CHO-AF by using the absolute ethyl alcohol, performing suction filtration to prepare fiber paper, and drying the fiber paper at the temperature of 80 ℃ to obtain the polyetheramine grafted alginate fiber (AF-PEA 2000).

Dissolving 2g of PEO and 0.4 g of LiTFSI in 40mL of anhydrous acetonitrile, uniformly stirring at room temperature by using a magnetic stirrer, pouring on AF-PEA2000, standing at room temperature for 12 hours for shaping, and then drying in vacuum at 65 ℃ for 24 hours to prepare the PEO @ AF-PEA2000 polymer electrolyte.

And (3) assembling the final product into an LFP/PEO @ AF-PEA2000/Li button cell by using a die cutting piece with the diameter of 15mm as a solid electrolyte, using lithium iron phosphate as a positive electrode and a lithium sheet as a negative electrode in a glove box, performing charge-discharge circulation on a blue cell test system at the temperature of 80 ℃ at the current density of 2C (1C =170mAh/g), and testing the impedance of the button cell formed according to the steps by using an electrochemical workstation at the temperature of 80 ℃. SS/PEO @ AF-PEA2000/Li button cell assembled with the above material PEO @ AF-PEA2000 using stainless steel sheet, lithium sheet was subjected to LSV test at 80 ℃ using an electrochemical workstation.

Claims (6)

1. A modification method of alginate fibers comprises the following steps:

1) Adding Alginate Fiber (AF) into HCl solution, standing for 1-4 hours at room temperature, and washing with water to obtain acidified alginate fiber;

2) Placing the product of the step 1) in deionized water at room temperature, adding sodium periodate aqueous solution into the deionized water, reacting for 12 to 24 hours in a dark place, and then washing the mixture with ethanol to obtain oxidized alginate fibers;

3) Placing the product of the step 2) in an organic solvent, adding polyetheramine into the organic solvent at room temperature for reaction, and then cleaning and drying the organic solvent to obtain polyetheramine grafted alginate fibers;

the dosage ratio of the alginate fiber to the sodium periodate is (1-10) g:0.1mmol;

the mass ratio of the alginate fibers to the polyether amine is 5-20: 1.

2. The modification process according to claim 1, wherein the HCl solution is a 1M HCl solution; the concentration of the sodium periodate aqueous solution is 1M; the organic solvent is absolute ethyl alcohol.

3. The modification process as claimed in claim 1, characterized in that the polyetheramine has a molecular weight of 230 to 2000.

4. The application of the polyether amine grafted alginate fiber prepared by the modification method of any one of claims 1 to 3 in a liquid diaphragm or a solid diaphragm of a lithium battery.

5. The application of claim 4, wherein the polyetheramine grafted alginate fiber prepared by the modification method of any one of claims 1 to 3 is used in a liquid separator of a lithium battery, and is directly cut into pieces according to required sizes and then put into lithium battery assembly to be used as the separator.

6. The use of the modified polyetheramine grafted alginate fiber of claim 4, wherein the modified polyetheramine grafted alginate fiber of claim 1 to 3 is used in solid separator of lithium battery, and the use comprises the following steps:

uniformly pouring a prepared mixed solution of polyethylene oxide (PEO) and lithium bistrifluoromethylsulfonyl imide (LiTFSI) on polyether amine grafted alginate fibers, air-drying and shaping at room temperature, and drying moisture in vacuum to obtain the lithium ion battery polymer solid electrolyte with the modified alginate fibers as a framework.

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