CN103474610A - Method for preparing composite lithium-ion battery separator through electrostatic spinning/electrostatic spraying - Google Patents

Abstract

The invention relates to the field of lithium-ion batteries, in particular to a method for preparing a multilayer composite lithium-ion battery separator by electrostatic spinning/electrostatic spraying. The specific steps of the method are: (1) the first step: adding the high molecular polymer into the organic solvent, mechanically stirring and dissolving to form a transparent solution, and obtaining an electrospinning solution; (2) polymerizing the inorganic nanoparticles and the high molecular (3) Electrospinning the spinning solution prepared in the first step to prepare the lower nanofiber membrane, and then the inorganic nanoparticle prepared in the second step The nanoparticle suspension is deposited on the lower nanofiber membrane by electrostatic spraying, which is the middle layer, and finally, a layer of electrospun nanofiber membrane is received on the inorganic particle layer to obtain a composite lithium-ion battery diaphragm. The lithium ion battery diaphragm prepared by the invention has high liquid absorption rate, good electrochemical stability and good heat shrinkage resistance at room temperature.

Description

A method for preparing composite lithium-ion battery diaphragm by electrospinning/electrostatic spraying

technical field

The invention relates to the field of lithium ion batteries, in particular to a method for preparing a multilayer composite lithium ion battery separator by electrostatic spinning/electrostatic spraying.

technical background

Lithium-ion batteries are mainly composed of positive and negative electrodes, separators, electrolytes and pole shells. Among them, the separator is between the positive and negative electrode materials, which plays the role of isolating the positive and negative electrodes, preventing short circuit, preventing electrons from passing through, and allowing ions to pass through. The performance of the separator determines the internal resistance and internal interface structure of the battery, which in turn affects the capacity, charge and discharge performance, cycle performance and safety performance of the battery.

Gel polymer electrolyte refers to the polymer network system formed by the swelling of the polymer separator after absorbing the electrolyte. It has the diffusion ability of liquid and the cohesiveness of solid, and is widely used in lithium-ion batteries. At present, the gel polymer electrolyte materials for lithium-ion batteries that have been studied more include polymethyl methacrylate (PMMA), polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF) and their copolymers. things etc.

In patent CN102790195A, inorganic ceramic particles are added to organic polymer solution to prepare a composite lithium-ion battery separator by casting method. silk to prepare organic/inorganic composite nanofiber lithium-ion battery diaphragm; but in the two diaphragm preparation methods provided above, the problem that inorganic particles are difficult to uniformly disperse in the organic solution will appear, and equipment such as a dispersant or a ball mill is required, and The uneven dispersion of inorganic particles will seriously affect the mechanical and electrochemical performance of the separator.

In patents WO2012050682A2, TW201230453A and US2012082884A1, composite nanofibers of P(VDF-HFP) and inorganic ceramic particles are directly deposited on positive or negative electrode materials by electrospinning. The diaphragm prepared by this method is directly compounded on the electrode material, and the thickness and uniformity of the diaphragm are limited to a certain extent, which is not conducive to online debugging in the production process. In addition, the compounding of the diaphragm and electrode material increases the complexity of the process, which is not conducive to production and processing. , is also not conducive to the optimal configuration of the separator and electrode materials.

In patents CN102820446, US2010/0316903A1 and US6432586B1, a porous layer composed of inorganic oxide particles and polymer organic matter or binder is coated on a microporous membrane substrate to prepare a lithium-ion battery composite separator. The composite membrane prepared by this method has a large thickness, low liquid absorption rate, and high internal resistance of the battery. During processing and use, the inorganic particles are easy to fall off and affect the performance of the battery. Patent CN102407623A proposes a method of sputtering inorganic oxides on both sides of an organic diaphragm by magnetron sputtering to prepare a composite lithium-ion battery diaphragm. In this method, the organic diaphragm needs to be placed in the magnetron sputtering cavity, and inorganic substances are sputtered on both sides of the diaphragm twice, so the production cannot be carried out continuously, and the efficiency is low.

Cho et al coated SiO ₂ or Al ₂ O ₃ particles on polyolefin fiber nonwovens, then received a layer of electrospun PAN nanofibers and then hot-rolled to prepare a three-layer composite lithium-ion battery separator (Cho T, Tanaka M, Ohnishi H, et al. Composite nonwoven separator for lithium-ion battery: Development and characterization [J]. Journal of Power Sources. 2010, 195(13): 4272-4277.). The composite diaphragm prepared by this method has large thickness, low porosity and low air permeability. Patent CN102751462A provides a method for preparing a composite diaphragm, which includes a support layer, an inorganic particle layer and a polytetrafluoroethylene layer, wherein the inorganic particle layer is located between the support layer and the polytetrafluoroethylene layer. The PTFE material used has low surface energy, poor wettability, poor compatibility and adhesion with other materials, it needs to be surface modified, and adhesion aids and A small amount of acid, the process is complicated, and the processing cost is high.

Contents of the invention

Aiming at the deficiencies of the prior art, the problem to be solved by the present invention is to provide a method for preparing a composite lithium-ion battery diaphragm by electrospinning/electrostatic spraying. The preparation process can be completed on the same electrospinning device to realize the continuous production of the composite membrane, the process is simple, the control is easy, the operation is convenient, and the cost is low.

The composite diaphragm prepared by the method of the present invention has a three-layer structure: the upper and lower layers are electrospun nanofiber membranes, and the inner layer is a nanoparticle layer deposited by electrostatic spraying. Chemical stability window.

The specific production steps are:

The first step: adding the high molecular polymer into the organic solvent, mechanical stirring and dissolving, forming a transparent solution, and preparing the electrospinning solution.

The second step: adding the mixture of inorganic nanoparticles and high molecular polymer into the organic solvent, stirring mechanically to prepare the suspension of inorganic nanoparticles.

The third step: Electrospinning the spinning solution prepared in the first step to prepare the lower nanofiber membrane; then the inorganic nanoparticle suspension prepared in the second step is electrostatically sprayed onto the lower nanofiber membrane to form the middle layer ; Finally, a layer of electrospun nanofiber membrane is received on the inorganic particle layer to obtain a composite lithium-ion battery separator.

Preferably, the polymer in the first step and the second step is one or a mixture of two or more of PMMA, PAN, PEO, PVDF and P(VDF-HFP).

Preferably, the organic solvent in the first step and the second step is N,N-dimethylformamide, N,N-dimethylacetamide, acetone, N-methylpyrrolidone, hexafluoroisopropanol , one or more mixtures of tetrahydrofuran.

Preferably, the inorganic nanoparticles in the second step are one or a mixture of two or more of Al ₂ O ₃ , SiO ₂ , TiO ₂ , BaTiO ₃ , MgO, ZrO ₂ , ZnO, and SiC.

Preferably, the electrospinning receiving device in the third step is one or more of aluminum foil, iron plate, iron mesh, copper mesh, iron roller, aluminum roller and non-woven material.

Preferably, the mass ratio of inorganic nanoparticles to high molecular polymers in the second step is: 0.9-0.95:0.1-0.05.

Preferably, the thickness of the composite separator prepared in the third step is 20-40 μm, wherein the thickness of the inorganic nanoparticle layer is 5-10 μm.

Compared with the prior art, the present invention has the advantages of:

1. The electrospinning/electrostatic spraying composite lithium-ion battery diaphragm prepared by the present invention has a mesh membrane structure composed of nanofibers with a high specific area on the upper and lower layers, and a microporous inorganic particle accumulation layer in the middle, which can store a large amount of of electrolyte. The composite film can quickly absorb the electrolyte, and the nanofiber layer of the outer layer is in a gel state to lock the electrolyte absorbed by the inorganic particle layer, and has a high liquid retention rate.

2. The method for preparing the electrospinning/electrostatic spraying lithium-ion battery diaphragm provided by the present invention does not use irrelevant substances that affect the electrochemical performance of the diaphragm, and the entire processing and preparation process is completed on the same electrospinning equipment, which can realize continuous production. The operation is convenient, the technological process is short, and the cost is low.

3. In the electrospinning/electrostatic spraying composite lithium-ion battery diaphragm prepared by the present invention, the inorganic particles are placed between two layers of nanofiber membranes, and there will be no shedding phenomenon during production and use.

4. The electrospinning/electrostatic spraying composite lithium-ion battery separator prepared by the present invention has low thermal shrinkage, good electrochemical stability and high porosity, and at the same time, the mechanical strength can meet the requirements of the battery assembly process.

5. The preparation process of the inorganic nanoparticle suspension in the electrospinning/electrostatic spraying composite lithium-ion battery diaphragm preparation method provided by the present invention is simple, and the uniformity of the nanoparticle suspension has little influence on the mechanical properties of the composite diaphragm.

Description of drawings

Figure 1 is a diagram of the preparation process of the electrospinning/electrostatic spray composite diaphragm, in which (1) is the preparation of the first layer of electrospinning membrane, (2) is the preparation of the second layer of electrostatic spray deposition inorganic particle layer, (3) is the third layer of electrostatic spraying Spun nanofiber layer preparation.

Figure 2 is the morphological structure diagram of the electrospinning/electrostatic spraying composite diaphragm, where a is the cross-sectional structure of the composite diaphragm, b is the outer nanofiber membrane, and c is the middle inorganic particle layer

Detailed ways

Specific examples of the present invention are given below. These specific examples are only used to further describe the present invention, and do not limit the protection scope of the claims of the present application.

Example 1

At room temperature, the dried PVDF was weighed and added to a certain amount of DMF/acetone mixed solvent, stirred and dissolved to prepare a polymer spinning solution. Then, nanometer Al ₂ O ₃ and PVDF (mass ratio 0.8:0.2) were weighed and added into DMF solvent to prepare nanoparticle suspension.

The polymer spinning solution is electrospun to prepare PVDF nanofiber membrane and deposited on the receiving device, then the nanoparticle suspension is deposited on the nanofiber membrane by electrostatic spraying, and then a layer of electrospun PVDF nanofiber is received on the inorganic particle layer. The fiber membrane, that is, the electrospinning/electrostatic spraying composite lithium-ion battery separator was obtained.

The prepared electrospinning/electrostatic spraying composite lithium-ion battery separator was placed in a hot box at 150°C for 1 hour, and the shrinkage rate was 1.25%. The fiber membrane was immersed in ethylene carbonate/dimethyl carbonate/dicarbonate of 1mol lithium hexafluorophosphate In the electrolyte solution of ethyl ester (mass ratio 1:1:1), the liquid absorption rate obtained is 496%, the ion conductivity is 1.83mS/cm, and the electrochemical stability window is 5.27V.

Example 2

At room temperature, the dried P(VDF-HFP) was weighed and added to a certain amount of DMF solvent, stirred and dissolved to prepare a polymer spinning solution. Then weigh nano-SiO ₂ and P(VDF-HFP) (mass ratio 0.9:0.1) and add them into DMF solvent to prepare nanoparticle suspension.

The P(VDF-HFP) nanofiber film prepared by electrospinning of the polymer spinning solution is deposited on the receiving device, and then the nanoparticle suspension is deposited on the nanofiber film by electrostatic spraying, and then a layer of inorganic particles is received on the inorganic particle layer. A layer of electrospun P (VDF-HFP) nanofiber membrane is obtained to obtain an electrospinning/electrostatic spraying composite lithium-ion battery separator.

The prepared electrospinning/electrostatic spraying composite lithium-ion battery diaphragm is placed in 150 ℃ of hot boxes to process 1h, and shrinkage rate is 1.36%, and this fiber membrane is immersed in the ethylene carbonate/dimethyl carbonate of 1mol lithium hexafluorophosphate /diethyl carbonate (mass ratio is 1:1:1) electrolyte, the liquid absorption rate obtained is 542%, the ion conductivity is 2.24mS/cm, and the electrochemical stability window is 5.32V.

Example 3

At room temperature, the dried PMMA was weighed and added to a certain amount of DMAc/acetone mixed solvent, stirred and dissolved to prepare a polymer spinning solution. Then weigh nanometer ZrO ₂ and PMMA (mass ratio 0.98:0.02) and add to DMAc solvent to prepare nanoparticle suspension.

The polymer spinning solution is electrospun to prepare the PMMA nanofiber film and deposited on the receiving device, and then the nanoparticle suspension is deposited on the nanofiber film by electrostatic spraying, and then a layer of electrospun PMMA nanofiber is received on the inorganic particle layer. The fiber membrane, that is, the electrospinning/electrostatic spraying composite lithium-ion battery separator was obtained.

The prepared electrospinning/electrostatic spray composite lithium-ion battery separator was placed in a hot box at 150°C for 1 hour, and the shrinkage rate was 0.94%. The fiber membrane was immersed in ethylene carbonate/dimethyl carbonate/dicarbonate of 1mol lithium hexafluorophosphate In the electrolyte solution of ethyl ester (mass ratio 1:1:1), the liquid absorption rate obtained is 478%, the ion conductivity is 1.62mS/cm, and the electrochemical stability window is 5.41V.

Example 4

At room temperature, the dried PAN was weighed and added to a certain amount of DMF/NMP mixed solvent, stirred and dissolved to prepare a polymer spinning solution. Then weigh nano TiO ₂ and PAN (mass ratio 0.95:0.05) and add them into DMAc solvent to prepare nanoparticle suspension.

The PAN nanofiber film prepared by electrospinning the polymer spinning solution is deposited on the receiving device, and then the nanoparticle suspension is deposited on the nanofiber film by electrostatic spraying, and then a layer of electrospun PAN nanofiber is received on the inorganic particle layer. The fiber membrane, that is, the electrospinning/electrostatic spraying composite lithium-ion battery separator was obtained.

The prepared electrospinning/electrostatic spraying composite lithium-ion battery separator was placed in a hot box at 150°C for 1 hour, and the shrinkage rate was 1.13%. The fiber membrane was immersed in ethylene carbonate/dimethyl carbonate/dicarbonate of 1mol lithium hexafluorophosphate In the electrolyte solution of ethyl ester (mass ratio 1:1:1), the liquid absorption rate obtained is 452%, the ion conductivity is 1.46mS/cm, and the electrochemical stability window is 5.14V.

Example 5

At room temperature, the dried PVDF and PAN were weighed and added to a certain amount of DMF/acetone mixed solvent, stirred and dissolved to prepare a polymer spinning solution. Then, nanometer SiC and PVDF (mass ratio 0.85:0.15) were weighed and added to DMAc solvent to prepare nanoparticle suspension.

The polymer spinning solution is electrospun to prepare PVDF/PAN nanofiber film and deposited on the receiving device, then the nanoparticle suspension is deposited on the nanofiber film by electrostatic spraying, and then a layer of electrospun is received on the inorganic particle layer. PVDF/PAN nanofiber membrane, that is, an electrospinning/electrostatic spraying composite lithium-ion battery separator was obtained.

The prepared electrospinning/electrostatic spraying composite lithium-ion battery separator was placed in a hot box at 150°C for 1 hour, and the shrinkage rate was 1.04%. The fiber membrane was immersed in ethylene carbonate/dimethyl carbonate/dicarbonate of 1mol lithium hexafluorophosphate In the electrolyte solution of ethyl ester (mass ratio 1:1:1), the liquid absorption rate obtained is 489%, the ion conductivity is 1.78mS/cm, and the electrochemical stability window is 5.23V.

Claims (7)

1. prepare the method for composite lithium ion cell barrier film by electrostatic spinning/electrostatic spray, it is characterized in that, concrete steps are:

The first step: high molecular polymer is joined in organic solvent, and mechanical agitation is dissolved, and forms clear solution, makes electrostatic spinning liquid;

Second step: inorganic nanoparticles and high polymer mixtures are joined in organic solvent, and mechanical agitation, make inorganic nanoparticles suspension;

The 3rd step: the spinning solution electrostatic spinning prepared in the first step is prepared to lower floor's nano fibrous membrane; The inorganic nanoparticles suspension prepared in second step being deposited on lower floor's nano fibrous membrane through electrostatic spray, is intermediate layer again; Finally, receive one deck electrostatic spinning nano fiber film on the inorganic particulate granulosa, make the composite lithium ion cell barrier film.

2. the method for preparing the composite lithium ion cell barrier film by electrostatic spinning/electrostatic spray as claimed in claim 1, it is characterized in that one or more the mixture that the high molecular polymer in the described first step and second step is PMMA, PAN, PVDF and P (VDF-HFP).

3. the method for preparing the composite lithium ion cell barrier film by electrostatic spinning/electrostatic spray as claimed in claim 1, it is characterized in that, organic solvent in the described first step and second step is N, the mixture of one or two or more kinds in dinethylformamide (DMF), DMA (DMAc), acetone, 1-METHYLPYRROLIDONE (NMP), hexafluoroisopropanol (HFIP), oxolane.

4. the method for preparing the composite lithium ion cell barrier film by electrostatic spinning/electrostatic spray as claimed in claim 1, is characterized in that, the inorganic nanoparticles in described second step is Al ₂o ₃, SiO ₂, TiO ₂, BaTiO ₃, MgO, ZrO ₂, one or two or more kinds the mixture in ZnO, SiC.

5. the method for preparing the composite lithium ion cell barrier film by electrostatic spinning/electrostatic spray as claimed in claim 1, is characterized in that, in described second step, the mass ratio of inorganic nanoparticles and high molecular polymer is: 0.8～0.98: 0.2～0.02.

6. the method for preparing the composite lithium ion cell barrier film by electrostatic spinning/electrostatic spray as claimed in claim 1, it is characterized in that, the electrostatic spinning receiving system in described the 3rd step is one or more in aluminium foil, iron plate, iron net, copper mesh, iron roller, aluminum drum and non-woven material.

7. the method for preparing the composite lithium ion cell barrier film by electrostatic spinning/electrostatic spray as claimed in claim 1, it is characterized in that, in described the 3rd step, the thickness of prepared composite diaphragm is 20～100 μ m, and wherein the thickness of inorganic nanoparticles layer is 5～20 μ n.

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