Functional composite diaphragm for battery and preparation method of functional composite diaphragm

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a functional composite diaphragm for a battery and a preparation method thereof, the functional composite diaphragm comprises a base membrane and a composite electrolyte, the composite electrolyte is formed by compounding a polymer and a solid electrolyte, and the formed composite electrolyte has a microporous structure; the polymer and the solid electrolyte are prepared from the following components in percentage by mass: a mixture of 5-95% of the solid electrolyte and 5-95% of the polymer is used as a solute, a dispersing agent is used as a solvent, the solid content of the dispersing agent is 10-70wt%, and the solute and the solvent are uniformly mixed. The solid content of the slurry is effectively improved, the use of solvents is reduced, and the production efficiency is improved; the composite electrolyte is in surface contact with the base membrane and is effectively filled in pores of the base membrane, and the base membrane can play a supporting role, so that the strength of the coated diaphragm is effectively improved, and the battery is convenient to assemble.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a functional composite diaphragm for batteries and a preparation method thereof. Technical Background

[0002] With the rapid development of electronic products, power tools, electric vehicles, energy storage and other industries, people have higher and higher requirements for the electrochemical properties and safety performance of lithium ions. As one of the four main materials of lithium-ion batteries, the traditional diaphragm plays the role of adsorbing electrolyte, providing an effective channel for lithium ions, blocking the short circuit of positive and negative electrodes, and closing the channel to prevent short circuit when the battery fails. At present, the diaphragm materials used commercially are mainly polyethylene (PE) and polypropylene (PP) or a composite material of the two. Although this material has the above functions, it is easy to fail or catch fire in the state of thermal runaway, and it is less effective in inhibiting lithium dendrites. In order to improve the above problems, researchers coated ceramic materials such as alumina on the surface of the diaphragm to inhibit the penetration of lithium dendrites, and coated materials such as polyvinylidene fluoride (PVDF) to improve the interface performance between the diaphragm and the pole piece. However, the above methods still cannot effectively prevent battery fires or lithium dendrite penetration.

[0003] In order to further improve the safety performance of lithium-ion batteries, researchers are considering replacing liquid electrolytes with solid electrolytes to develop lithium batteries with higher specific capacity and better safety. However, although pure ceramic solid electrolytes have high ionic conductivity, the interface contact with the electrodes is poor, the interface contact resistance is large, and the formed ceramic sheets are fragile, which is not conducive to the flexibility of the device. The preparation process of polymer electrolytes is simple and easy to operate, has good flexibility, and can improve the interface contact with the electrodes to a certain extent. However, the mechanical properties of polymer electrolytes are poor and the lithium ion conductivity is low, making it difficult to exert the excellent electrochemical properties of the battery.

[0004] In order to solve the existing shortcomings of the two electrolytes, the researchers adopted the method of combining polymers and solid electrolytes, hoping to suppress the shortcomings of each of them and make full use of the advantages of both. The preparation of composite membranes usually adopts spraying method, casting method, etc. Although the above method can combine the two electrolytes together, there are still difficulties such as poor mechanical properties of the electrolyte, the thickness of the electrolyte is difficult to achieve below 100 microns, low battery energy density, and complex battery processing technology. In addition, coating methods such as spraying and scraping require the mixed liquid to have good fluidity, increase the solvent content, and reduce the solid content. In addition, the composite membrane prepared by traditional casting method, scraping, spraying, filtration, etc. will cause the composite membrane to shrink and produce holes during the drying process, and there is a risk that lithium dendrites will easily pierce the diaphragm, thus posing a safety hazard. Summary of the invention

[0005] The present invention provides a functional composite diaphragm for a battery and a preparation method thereof, which can solve the problems pointed out in the background technology.

[0006] A functional composite diaphragm for a battery and a preparation method thereof, comprising a base film and a composite electrolyte, wherein the composite electrolyte is composited by a polymer and a solid electrolyte, and the formed composite electrolyte has a microporous structure; the polymer and the solid electrolyte are calculated according to the following mass percentages: a mixture of 20-80% of the solid electrolyte and 20-80% of the polymer is used as a solute, a dispersant is used as a solvent, and its solid content is 10-70wt%, and the solute and the solvent are uniformly mixed.

[0007] Preferably, the solid electrolyte is one or more of solid oxide, sulfide, and halogen electrolyte.

[0008] Preferably, the polymer is one or more of poly(vinylidene fluoride-co-hexafluoropropylene), polyethylene oxide, polyacrylonitrile, polyvinyl alcohol, and polyethylene glycol.

[0009] Preferably, the solvent is one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, diethylene glycol methyl ether, ethyl acetate, ethanol, isopropanol, methanol and water.

[0010] Preferably, the base film is a PE base film or a PP base film or a composite base film of PE and PP or a glass fiber base film, and a polymer / solid electrolyte coating is provided inside the gaps and on the surface of the base film, and the thickness of the base film is 5-100 μm.

[0011] Preferably, the composite electrolyte is composited with the base membrane by 3D printing or electrostatic spinning, and the composite electrolyte has a thickness of 1-150 μm after drying.

[0012] Preferably, the solute and the solvent are uniformly mixed by stirring or ball milling.

[0013] Beneficial effects:

[0014] (1) The mixture of polymer / solid electrolyte and solvent can be instantly solidified after being processed by 3D printing, electrospinning and other technologies, avoiding the generation of voids and effectively improving the safety performance of the battery;

[0015] (2) Compared with coating methods such as spraying and scraping, the present invention can effectively increase the solid content of the slurry, reduce the use of solvents, and improve production efficiency.

[0016] (3) The composite electrolyte is in surface contact with the base membrane and is effectively filled in the pores of the base membrane. The base membrane can play a supporting role, effectively improving the strength of the coated diaphragm and facilitating the assembly of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Composite electrolyte prepared by tape casting

[0018] Figure 2 Preparation of composite electrolyte / diaphragm by 3D printing

[0019] Figure 3 Preparation of composite electrolyte / diaphragm by 3D printing in a bent state

[0020] Figure 4 Composite electrolyte / diaphragm surface SEM image Specific implementation method

[0021] Figure 5 Discharge curves of button batteries in the embodiments and comparative examples

[0022] Figure 6 Cycle curves of button batteries in the examples and comparative examples DETAILED DESCRIPTION

[0023] A specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific implementation.

[0024] Combination Figure 1-6 As shown, all embodiments of the present invention and the comparative examples are different in that the preparation of lithium-ion batteries adopts the following process except for the diaphragm: lithium iron phosphate is used as the positive electrode material, and the positive electrode material, conductive carbon black, and polyvinylidene fluoride are weighed in a mass ratio of 90:5:5, and the weighed materials are mixed evenly with N-methylpyrrolidone and then coated on aluminum foil, and then dried and cut into the size required by the process; hard carbon, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber are weighed in a mass ratio of 90:5:2.5:2.5, and the weighed materials are mixed evenly with deionized water and then coated on copper foil, and then dried and cut into the size required by the process. The positive electrode sheet, diaphragm, and negative electrode sheet are made into button batteries.

[0025] The prepared button battery was charged and discharged at a current density of 1C, with a charge and discharge cut-off voltage of 2.0-3.65V. The discharge curve and charge and discharge cycle curve were as follows: Figure 4 and Figure 5 shown.

[0026] Example 1

[0027] The lithium aluminum titanium phosphate solid electrolyte and poly (vinylidene fluoride-co-hexafluoropropylene) were weighed in a mass ratio of 7:3, put into N-methylpyrrolidone and evenly dispersed by ball milling, and the obtained slurry was coated on the surface and gap of PP by 3D printing. The prepared diaphragm was Figure 2 and 3As shown, the electrolyte on the surface of the separator is Figure 4 As shown, the positive electrode sheet, the coated separator, and the negative electrode sheet are made into a button battery.

[0028] Example 2

[0029] The lithium aluminum titanium phosphate solid electrolyte and poly (vinylidene fluoride-co-hexafluoropropylene) were weighed at a mass ratio of 8:2, and were placed in N, N-dimethylacetamide and evenly dispersed by vacuum stirring. The obtained slurry was coated on the PP surface and gaps by 3D printing. The positive electrode sheet, coated separator, and negative electrode sheet were made into button batteries.

[0030] Example 3

[0031] Lithium lanthanum zirconium titanium oxide solid electrolyte and polyethylene oxide were weighed at a mass ratio of 2:8, placed in N,N-dimethylformamide and mixed evenly by double planetary stirring. The obtained slurry was coated on the PE surface and gaps by electrospinning. The positive electrode sheet, coated diaphragm, and negative electrode sheet were made into button batteries.

[0032] Comparative Example 1

[0033] Lithium lanthanum zirconium titanium oxide solid electrolyte and polyethylene oxide were weighed in a mass ratio of 7:3, placed in N, N-dimethylformamide and mixed evenly by double planetary stirring. The obtained slurry was placed in a culture dish by tape casting and vacuum dried at 60°C for 24 hours. The thickness of the obtained composite electrolyte was about 100μm, but the electrolyte was fragile ( Figure 1 As shown in the figure, the button cell used for preparing battery separator has poor cycle performance.

[0034] The above disclosures are only several specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A functional composite diaphragm for a battery and a preparation method thereof, characterized in that: The invention comprises a base film and a composite electrolyte, wherein the composite electrolyte is composited by a polymer and a solid electrolyte, and the composite electrolyte has a microporous structure; the polymer and the solid electrolyte are calculated according to the following mass percentages: a mixture of 5-95% of the solid electrolyte and 5-95% of the polymer is used as the solute, a dispersant is used as the solvent, and the solid content thereof is 10-70wt%, and the solute and the solvent are uniformly mixed.

2. A functional composite diaphragm for a battery and a method for preparing the same according to claim 1, characterized in that: The solid electrolyte is one or more of solid oxide, sulfide and halogen electrolyte.

3. A functional composite diaphragm for a battery and a method for preparing the same according to claim 1, characterized in that: The polymer is one or more of poly(vinylidene fluoride-co-hexafluoropropylene), polyethylene oxide, polyacrylonitrile, polyvinyl alcohol, and polyethylene glycol.

4. A functional composite diaphragm for a battery and a method for preparing the same according to claim 1, characterized in that: The solvent is one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, diethylene glycol methyl ether, ethyl acetate, ethanol, isopropanol, methanol and water.

5. A functional composite diaphragm for a battery and a method for preparing the same according to claim 1, characterized in that: The base film is a PE base film or a PP base film or a composite base film of PE and PP or a glass fiber base film, and a polymer / solid electrolyte coating is arranged inside the gaps and on the surface of the base film. The thickness of the base film is 5-100 μm.

6. A functional composite diaphragm for a battery and a method for preparing the same according to claim 1, characterized in that: The composite electrolyte is composited with the base membrane by 3D printing or electrostatic spinning, and the thickness of the composite electrolyte after drying is 1-150 μm.

7. A functional composite diaphragm for a battery and a method for preparing the same according to claim 1, characterized in that: The solute and the solvent are uniformly mixed by stirring or ball milling.

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