CN111370624A - A kind of preparation method of commercial lithium ion battery modified separator - Google Patents

Abstract

The invention relates to a preparation method of a commercial lithium ion battery modified diaphragm, which comprises the following steps: firstly, dissolving polyelectrolyte in a solvent to prepare a polyelectrolyte solution with the mass fraction of 0.1-20 wt%, then adding a proper amount of ultraviolet crosslinking monomer, and uniformly stirring to obtain a mixed solution; then spraying the mixed solution on a commercial lithium battery diaphragm in an electrostatic spraying or electrostatic spinning mode; and finally, crosslinking the commercial lithium battery diaphragm under ultraviolet irradiation for 1-300 min, and drying in vacuum for 6-72h at the temperature of 30-100 ℃ to obtain the surface modified diaphragm. The method has wide application range, is simple and easy to implement, is environment-friendly, can realize direct modification of the hydrophobic commercial diaphragm by the hydrophilic polymer, can realize fine regulation and control of the surface functional layer of the diaphragm, and is suitable for large-scale production.

Description

A kind of preparation method of commercial lithium ion battery modified separator

technical field

The invention relates to a method for modifying a diaphragm, in particular to a method for preparing a modified diaphragm of a commercial lithium ion battery.

Background technique

With the development of new energy vehicles and high energy density batteries, the lithium battery market has ushered in opportunities for rapid development, and at the same time, higher requirements have been placed on the comprehensive performance of lithium batteries. Lithium batteries are mainly composed of four parts: positive electrode material, negative electrode material, separator and organic electrolyte. Separator plays a vital role in Li-ion batteries, it can prevent short circuit problems caused by direct contact between positive and negative materials, and can provide a channel for the transport of lithium ions between positive and negative materials. Therefore, the performance of the separator is very important, which directly affects the capacity, cycle life and safety performance of the battery.

In addition to electronic insulation and mechanical isolation, the diaphragm should also have the following characteristics: 1) good chemical and electrochemical stability, resistance to corrosion of electrolyte and electrode materials; 2) good electrolyte wettability, and sufficient Liquid absorption and moisturizing ability; 3) Good mechanical properties to prevent short circuit caused by burrs, dendrites or foreign objects punctured; 4) Good thermal stability; 5) Has a certain pore size and porosity to ensure low resistance and high high ionic conductivity and good permeability to lithium ions.

At present, the commonly used commercial battery separators are mainly polyolefin (such as polypropylene, polyethylene, etc.) microporous films, which have excellent mechanical properties and chemical stability. However, since polyolefin-based microporous membranes are mostly made by the stretching film-forming process, such membranes have the disadvantages of low porosity, poor wettability, low ionic conductivity, poor puncture resistance and oxidation resistance. As a result, the battery using this separator has a huge potential safety hazard, which can no longer meet the use requirements of today's 3C products and power batteries, which seriously restricts the development of lithium-ion batteries. In addition, the polyolefin molecular chain in the polyolefin-based microporous membrane does not contain functional groups, is hydrophobic, and has poor wettability to the electrolyte, so the cycle stability of the commercial lithium-ion battery separator in the battery is poor. Therefore, the development of high-performance separators that can meet high-end market applications has become an urgent need for the lithium battery industry. It is understood that surface coating and modification of commercial battery separators is an effective solution. However, due to the hydrophobic surface of commercial battery separators, the current coating layers are all applied in the form of mud, and aqueous solutions of polymers (especially is a dilute solution) is difficult to be directly coated evenly.

SUMMARY OF THE INVENTION

The purpose of the present invention is: in view of the above-mentioned deficiencies in the prior art, a preparation method of a commercial lithium ion battery modified diaphragm is proposed. The modified coating prepared by the method can strengthen and stabilize the SEI film, so as to inhibit the charging and discharging process. Formation and growth of lithium dendrites.

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

A preparation method of a commercial lithium-ion battery modified separator, comprising the following steps:

(1) Dissolving the polyelectrolyte in a solvent to prepare a polyelectrolyte solution with a mass fraction of 0.1-40 wt%, then adding an appropriate amount of ultraviolet light cross-linking monomer, stirring uniformly, to obtain a mixed solution;

(2) spraying the mixed solution prepared in step (1) onto a commercial lithium battery separator by electrostatic spraying or electrospinning;

(3) Crosslinking the commercial lithium battery separator obtained in step (2) under ultraviolet light irradiation, the irradiation time is 1-300 min, and then vacuum drying at 30-100° C. for 6-72 h to obtain a surface-modified separator .

The invention adopts the combination of electrospinning (spraying) and photopolymerization to construct an ultra-thin hydrophilic and lithiophilic functional barrier layer on the surface of a commercial separator. A homogeneous solution is prepared in a solvent, electrospinning (spraying) is performed, and nanofibers (particles) are sprayed on a commercial separator; then it is cured and cross-linked under ultraviolet light, and dried in a vacuum oven for 6-72 hours. Modified commercial separator. A functional layer is constructed on the surface of the commercial separator to improve the wettability to the electrolyte. The functional layer of the present invention selects a lithiophilic charged polymer, which can effectively regulate lithium ion transport on the one hand, and participate in the formation of a stable SEI film (solid electrolyte membrane) on the other hand, thereby effectively inhibiting the charging and discharging process of lithium ion batteries. The generation and growth of lithium dendrites are beneficial to prolong the service life of the battery; since most lithiophilic charged polymers are water-soluble polymers, it is difficult to uniformly coat them on the hydrophobic commercial separator by ordinary methods. The spinning (spraying) technology directly sprays the hydrophilic material on the commercial separator to modify it. The thickness of the modified layer can be effectively controlled by controlling the time of electrospinning (spraying), which overcomes the difficulty in coating the hydrophilic material. The shortcomings of the modified commercial diaphragm, especially when the surface of the diaphragm is coated with an aqueous polymer solution; the functional layer construction of the present invention adopts the advantages of an aqueous solution, which is environmentally friendly, safe and pollution-free, while the traditional method of using organic reagents to form a thick slurry pollutes the environment. At the same time, the coating thickness is difficult to control; the present invention adopts the method of electrospinning or electrostatic spraying to uniformly spray the diluted charged polymer aqueous solution on the hydrophobic commercial separator. Realize the fine control of the thickness of the functional barrier layer. The functional layer of the present invention adopts the method of physical cross-linking, on the one hand, it does not consume the lithiophilic functional group, and on the other hand, the density of the functional layer is appropriate, so as to prevent the too dense functional layer from hindering the transport of lithium ions; The cross-linking adopts the semi-interpenetrating network technology, that is, the macromolecules generated by the monomer small molecules are induced by ultraviolet light irradiation to form a semi-interpenetrating network structure with the lithiophilic charged polymer, on the one hand, the physical cross-linking of the lithiophilic charged substances is realized. On the other hand, the semi-interpenetrating network formed has certain strength and flexibility, which can prevent lithium dendrites from piercing the separator during charging and discharging, so as to cope with the problem of volume expansion during charging and discharging.

The further refined technical scheme of the present invention is as follows:

Preferably, the polyelectrolyte is a polycation electrolyte or a polyanion electrolyte.

Preferably, the polycationic electrolyte is at least one of chitosan, polyethyleneimine, polyamide, polyvinylamine, polyvinylpyrrolidone, polyvinylpyridine, and polydimethyldiallylammonium chloride.

Preferably, the polyanion electrolyte is at least one of sodium polyacrylate, polymethacrylic acid, sodium alginate, sodium carboxymethylcellulose, polymetaphosphoric acid, polyvinylphosphoric acid, polystyrene sulfonic acid and polyvinyl sulfonic acid A sort of.

In the step (1), the polyelectrolyte solution and the spinning assistant can be mixed in a mass ratio of 1:(0.01-10), and then the ultraviolet light cross-linking monomer is added to the mixed solution; the spinning assistant is a polymer. One of ethylene oxide, polyvinyl alcohol, polyamide or polyacrylic acid.

It can be seen from the above that a spinning aid can be added or not added to the polyelectrolyte solution in step (1), and the purpose of adding a spinning aid is to make the electrospinning or electrospray more stable to obtain a stable jet.

Preferably, the ultraviolet light crosslinking monomer is polyacrylate, isooctyl acrylate, butyl acrylate, triethylene glycol dimethacrylate, tripropylene glycol diacrylate, 1,3-butane Glycol Dimethacrylate, Dicyclopentadienyl Acrylate, Diethylene Glycol Dimethacrylate, Pentaerythritol Tetramethacrylate, Trimethylolpropane Trimethacrylate, Hexylene Glycol Diacrylate, At least one of isobornyl acrylate, urethane acrylate, epoxy acrylate, and polyethylene glycol diglycidyl ether.

Preferably, the solvent is deionized water or an aqueous acetic acid solution, and the mass fraction of the aqueous acetic acid solution is 0.1-50 wt %.

Preferably, the commercial lithium battery separator is a commercial polyolefin separator or a polytetrafluoroethylene film.

Preferably, in the step (1), the mass ratio of the polyelectrolyte solution to the ultraviolet light crosslinking monomer is 1:(0.01-5).

Preferably, in the step (2), the process parameters of electrostatic spraying or electrospinning are a voltage of 8 to 40 kV, a nozzle diameter of 0.2 to 3 mm, a solution flow rate of 5 to 50 μl/min, and an ambient temperature of 10 to 60 °C. , the relative air humidity is 30 to 60%.

The modified separator prepared by the present invention is used for electrochemical performance test. The test results show that the running time of the Li/Li symmetrical battery with the modified separator is much longer than that of the battery with the unmodified separator, and the specific capacity of the Li/LiFePO ₄ battery after a long cycle is much higher than that of the battery with the unmodified separator. Batteries with unmodified separators.

Compared with the prior art, the present invention has the following advantages: the present invention selects a lithiophilic charged polymer to perform functional modification on the surface of the commercial lithium battery separator, participates in the formation of a stable SEI film, and can effectively inhibit the charging and discharging process of the lithium ion battery. The formation and growth of dendrites can obtain high-performance and high-stability lithium batteries, which is beneficial to prolong the service life of the batteries. The invention adopts electrostatic spraying or spinning method, which overcomes the disadvantage that the traditional coating method is difficult to coat uniformly.

In a word, the method of the present invention has a wide range of application, is simple and easy to operate, and is environmentally friendly, can realize the direct modification of a hydrophobic commercial diaphragm by a hydrophilic polymer, and can realize the fine control of the surface functional layer of the diaphragm, and is suitable for large-scale production. .

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings.

Fig. 1 shows the electrochemistry of the Li/Li battery before and after the electrostatic spraying of the chitosan solution on the surface of the Celgard commercial separator in Example 1 of the present invention under the conditions of a current density of 2 mA cm ^-2 and a rated capacity of 1.0 mAh cm ^-2 Cycle performance graph.

Figure 2 is a graph showing the long-term cycle performance of Li/LiFePO ₄ batteries before and after electrostatic spraying of chitosan solution on the surface of Celgard commercial separators at a current density of 10C (1750 mA g ^-1 ) in the embodiment of the present invention.

Detailed ways

The present invention will be described in detail below with reference to the embodiments and accompanying drawings of the description. Unless otherwise specified, the “solution” involved in the present invention is an aqueous solution formed by dissolving various substances in deionized water. The materials and reagents involved in the present invention are all common materials and reagents that can be purchased in the market.

Example 1

A method of using chitosan to modify the Celgard commercial diaphragm, specifically comprising the following steps:

1. Dissolve chitosan in an aqueous solution of acetic acid with a mass fraction of 1 wt% to prepare a chitosan solution with a mass fraction of 1.0 wt%, and then mix the chitosan solution with the spinning aid polyethylene oxide (PEO) according to mass. Mix evenly at a ratio of 1:0.11 to obtain a mixed solution;

2. Mix the mixed solution of step 1 with triethylene glycol dimethacrylate according to a mass ratio of 1:0.25, and stir evenly to obtain an electrostatic spray solution;

3. Add the electrostatic spray solution into the syringe, and control the extrusion by a micro-injection pump. The nozzle of the syringe is connected to a high-voltage positive electrode. The electrostatic spray parameters are controlled at a voltage of 26 kv, a nozzle diameter of 0.7 mm, a solution flow rate of 10 μl/min, and an ambient temperature of 30 °C. , the relative air humidity is 30%, electrostatic spray is carried out on the Celgard commercial diaphragm, and the electrostatic spray time is controlled to 20 min;

4. The separator obtained in step 3 was irradiated with ultraviolet light for 1 h, and then dried in a vacuum drying oven at a temperature of 40 °C for 24 h to obtain a modified separator, namely the CTS-PEO-PTEGDMA@Celgard separator.

5. The Li-Li electrochemical performance test was carried out on the modified separator, and it was found that the Li-Li long-cycle running time of the battery installed with the modified separator was 3.4 times that of the unmodified Celgard commercial separator. The electrochemical performance test of Li/LiFePO ₄ was carried out on the modified separator, and it was found that the capacity of Li/LiFePO ₄ of the battery loaded with the modified separator was more than 2 times that of the unmodified Celgard commercial separator after long-cycle operation of 1000 h.

Example 2

A method for modifying Celgard commercial diaphragm with sodium polyacrylate, specifically comprising the following steps:

1. Dissolve sodium polyacrylate in deionized water to prepare a sodium polyacrylate solution with a mass fraction of 2.5 wt%;

2. Mix the sodium polyacrylate solution in step 1 with diethylene glycol dimethacrylate according to a mass ratio of 1:0.12, and stir evenly to obtain an electrospinning solution;

3. Add the electrospinning solution to the syringe and extrude it under the control of a micro-injection pump. The nozzle of the syringe is connected to a high-voltage positive electrode. The electrostatic spray parameters are controlled at a voltage of 18 kv, a nozzle diameter of 0.7 mm, a solution flow rate of 15 μl/min, and an ambient temperature of 30 ℃, the relative air humidity is 30%, electrospinning is carried out on Celgard commercial diaphragm, and the electrostatic spray time is controlled to 15 min;

4. Irradiate the diaphragm obtained in step 3 under ultraviolet light for 120 min, and then dry it in a vacuum drying oven at 40°C for 24 hours to obtain a modified diaphragm;

5. The Li-Li electrochemical performance test was carried out on the modified separator, and it was found that the Li-Li long-cycle running time of the battery loaded with the modified separator was twice that of the unmodified Celgard commercial separator.

Example 3

A method for modifying Celgard commercial diaphragm by polyvinylpyridine, specifically comprising the following steps:

1. Dissolve polyvinylpyridine in deionized water to prepare a polyvinylpyridine solution with a mass fraction of 15 wt%;

2. Mix the polyvinylpyridine solution in step 1 with polyethylene glycol diglycidyl ether according to a mass ratio of 1:0.5, and stir evenly to obtain an electrospinning solution;

3. Add the electrospinning solution to the syringe and extrude it under the control of a micro-injection pump. The nozzle of the syringe is connected to a high-voltage positive electrode. The electrostatic spray parameters are controlled at a voltage of 12 kv, a nozzle diameter of 0.7 mm, a solution flow rate of 12 μl/min, and an ambient temperature of 30 ℃, the relative air humidity is 30%, electrospinning is carried out on Celgard commercial diaphragm, and the electrostatic spray time is controlled to 10 min;

4. Irradiate the diaphragm obtained in step 3 under ultraviolet light for 5 hours, and then dry it in a vacuum drying oven at 40°C for 24 hours to obtain a modified diaphragm;

5. The Li-Li electrochemical performance test was carried out on the modified separator, and it was found that the Li-Li long-cycle running time of the battery loaded with the modified separator was more than 1.8 times that of the unmodified Celgard commercial separator.

Example 4

A method for modifying Celgard commercial diaphragm by polydimethyldiallyl ammonium chloride, specifically comprising the following steps:

1. Dissolve polydimethyldiallyl ammonium chloride in deionized water, prepare a polydimethyldiallyl ammonium chloride solution with a mass fraction of 2 wt%, and then mix polydimethyldiallyl ammonium chloride. The base ammonium chloride solution and the polyethylene oxide spinning aid are mixed according to the mass ratio of 1:0.5 to form a uniform solution;

2. Mix the homogeneous solution in step 1 with pentaerythritol tetramethacrylate according to a mass ratio of 1:1, and stir to obtain an electrostatic spray solution;

3. Add the electrostatic spray solution into the syringe, control the extrusion by a micro-injection pump, the nozzle of the syringe is connected to a high-voltage positive electrode, the electrostatic spray parameters are controlled at a voltage of 26 kv, the nozzle aperture is 1.2 mm, the solution flow rate is 5 μl/min, and the ambient temperature is 20 ℃ , the relative air humidity was 40%, electrospinning was carried out on a Celgard commercial diaphragm, and the electrostatic spray time was controlled to 20 min;

4. Irradiate the diaphragm obtained in step 3 under ultraviolet light for 240 minutes, and then dry it in a vacuum drying oven at 50°C for 12 hours to obtain a modified diaphragm;

5. The Li-Li electrochemical performance test was carried out on the modified separator, and it was found that the Li-Li long-cycle running time of the battery with the modified separator was more than 1.5 times that of the unmodified Celgard commercial separator.

Example 5

A method for modifying Celgard commercial diaphragm with sodium carboxymethyl cellulose, specifically comprising the following steps:

1. Dissolve sodium carboxymethyl cellulose in deionized water to prepare a sodium carboxymethyl cellulose solution with a mass fraction of 5 wt%, and then mix sodium carboxymethyl cellulose solution and polyethylene oxide spinning aid according to the mass. Mix at a ratio of 1:1 to form a homogeneous solution;

2. Mix the uniform solution in step 1 with isobornyl acrylate in a mass ratio of 1:1.5, and stir evenly to obtain an electrostatic spray solution;

3. Add the electrostatic spray solution to the syringe, control the extrusion by a micro-injection pump, the nozzle of the syringe is connected to a high-voltage positive electrode, the electrostatic spray parameters are controlled at a voltage of 32kv, the nozzle hole diameter is 1.6mm, the solution flow rate is 30μl/min, and the ambient temperature is 10 ℃. The relative air humidity was 35%, electrospinning was carried out on Celgard commercial diaphragm, and the electrostatic spraying time was controlled to 10min;

4. Irradiate the diaphragm obtained in step 3 under ultraviolet light for 180 minutes, and then dry it in a vacuum drying oven at 30°C for 72 hours to obtain a modified diaphragm;

5. The Li-Li electrochemical performance test was carried out on the modified separator, and it was found that the Li-Li long-cycle running time of the battery loaded with the modified separator was 1.2 times that of the unmodified Celgard commercial separator.

Example 6

A method for modifying Celgard commercial diaphragm by polyamide and polyvinylamine, specifically comprising the following steps:

1. Dissolve polyamide and polyvinylamine (the mass ratio of the two is 1:1) in an aqueous solution with a mass fraction of 30wt% to prepare a mixed solution of polyethyleneimine and polyvinylamine with a mass fraction of 30%;

2. Mix the polyamide and polyvinylamine mixed solution of step 1 with the mixture of tripropylene glycol diacrylate and 1,3-butanediol dimethacrylate according to the mass ratio of 1:3, and stir evenly to obtain static electricity. Spray solution; wherein the mass ratio of tripropylene glycol diacrylate and 1,3-butanediol dimethacrylate is 1:1;

3. Add the electrostatic spray solution into the syringe, control the extrusion by a micro-injection pump, the nozzle of the syringe is connected to a high-voltage positive electrode, the electrostatic spray parameters are controlled at a voltage of 30kv, the nozzle aperture is 3mm, the solution flow rate is 25μl/min, the ambient temperature is 50°C, and the air The relative humidity was 60%, electrospinning was carried out on Celgard commercial diaphragm, and the electrostatic spray time was controlled to 10min;

4. Irradiate the diaphragm obtained in step 3 under ultraviolet light for 20 minutes, and then dry it in a vacuum drying oven at 70°C for 36 hours to obtain a modified diaphragm;

5. The Li-Li electrochemical performance test was carried out on the modified separator, and it was found that the Li-Li long-cycle running time of the battery with the modified separator was more than 1.5 times that of the unmodified Celgard commercial separator.

In addition to the above embodiments, the present invention can also have other embodiments, for example, the ultraviolet light cross-linking monomer can also be polyacrylate, dicyclopentadienyl acrylate, trimethylolpropane trimethacrylate, hexanediol Acrylic or urethane acrylate. All technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims (10)

1. a preparation method of commercial lithium ion battery modified diaphragm, is characterized in that, comprises the following steps: (1) Dissolving the polyelectrolyte in a solvent to prepare a polyelectrolyte solution with a mass fraction of 0.1-20 wt%, then adding an appropriate amount of ultraviolet light cross-linking monomer, stirring uniformly, to obtain a mixed solution; (2) spraying the mixed solution prepared in step (1) onto a commercial lithium battery separator by electrostatic spraying or electrospinning; (3) Crosslinking the commercial lithium battery separator obtained in step (2) under ultraviolet light irradiation, the irradiation time is 1-300 min, and then vacuum drying at 30-100° C. for 6-72 h to obtain a surface-modified separator . 2 . The preparation method of a commercial lithium-ion battery modified separator according to claim 1 , wherein the polyelectrolyte is a polycation electrolyte or a polyanion electrolyte. 3 . 3. the preparation method of a kind of commercial lithium-ion battery modified diaphragm according to claim 2, is characterized in that, described polycationic electrolyte is chitosan, polyethyleneimine, polyamide, polyvinylamine, polyvinylpyrrolidone , at least one of polyvinylpyridine and polydimethyldiallyl ammonium chloride. 4. the preparation method of a kind of commercial lithium ion battery modified diaphragm according to claim 2, is characterized in that, described polyanion electrolyte is sodium polyacrylate, polymethacrylic acid, sodium alginate, sodium carboxymethyl cellulose , at least one of polymetaphosphoric acid, polyvinylphosphoric acid, polystyrene sulfonic acid and polyvinyl sulfonic acid. 5 . The method for preparing a modified separator for commercial lithium ion batteries according to claim 1 , wherein in the step (1), the polyelectrolyte solution and the spinning aid can be mixed according to 1: (0.01-10) 5 . The mass ratio is mixed, and then the ultraviolet light cross-linking monomer is added to the mixed solution; the spinning assistant is one of polyethylene oxide, polyvinyl alcohol, polyamide or polyacrylic acid. 6. the preparation method of a kind of commercial lithium ion battery modified diaphragm according to claim 1, is characterized in that, described ultraviolet light cross-linking monomer is polyacrylate, isooctyl acrylate, butyl acrylate, tri-diacetate Ethylene Glycol Dimethacrylate, Tripropylene Glycol Diacrylate, 1,3-Butanediol Dimethacrylate, Dicyclopentadienyl Acrylate, Diethylene Glycol Dimethacrylate, Pentaerythritol Tetramethyl At least one of base acrylate, trimethylolpropane trimethacrylate, hexanediol diacrylate, isobornyl acrylate, urethane acrylate, epoxy acrylate, and polyethylene glycol diglycidyl ether. 7 . The method for preparing a modified diaphragm of a commercial lithium ion battery according to claim 1 , wherein the solvent is deionized water or an aqueous acetic acid solution, and the mass fraction of the aqueous acetic acid solution is 0.1 to 50 wt %. 8 . 8 . The preparation method of a commercial lithium-ion battery modified diaphragm according to claim 1 , wherein the commercial lithium battery diaphragm is a commercial polyolefin diaphragm or a polytetrafluoroethylene film. 9 . 9. the preparation method of a kind of commercial lithium ion battery modified diaphragm according to claim 1, is characterized in that, in described step (1), the mass ratio of polyelectrolyte solution and ultraviolet light cross-linking monomer is 1: ( 0.01～5). 10 . The method for preparing a modified separator for commercial lithium-ion batteries according to claim 1 , wherein in the step (2), the process parameters of electrostatic spraying or electrospinning are a voltage of 8-40 kV, a nozzle of The pore size is 0.2-3 mm, the solution flow rate is 5-50 μl/min, the ambient temperature is 10-60 ℃, and the relative air humidity is 30-60%.

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