Aqueous organic-inorganic composite diaphragm for lithium battery and preparation method of aqueous organic-inorganic composite diaphragm

Abstract

The invention relates to an aqueous organic-inorganic composite diaphragm for a lithium battery and a preparation method of the aqueous organic-inorganic composite diaphragm. The aqueous organic-inorganic composite diaphragm for the lithium battery consists of an organic polymer, an inorganic ceramic filler and a polyolefin diaphragm. According to the technical scheme, an organic polymer and an inorganic ceramic filler are prepared into aqueous slurry by using a small amount of a dispersing agent and a surfactant, and the organic-inorganic composite diaphragm is prepared by a dip-coating method and is applied to the lithium battery. According to the invention, the diaphragm of the lithium battery is modified, so that the wettability of the diaphragm to electrolyte is improved, the liquid absorption rate of the diaphragm is improved, and the transmission of lithium ions is promoted. And meanwhile, the thermal stability of the diaphragm is also improved. The excellent electrochemical performance of the lithium battery under the conditions of high current density and long-time high-temperature storage is realized. And the preparation process of the aqueous organic-inorganic composite diaphragm is simple, the electrochemical performance and the storage performance can be improved through simple steps, and large-scale production is easy to realize.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a water-based organic-inorganic composite diaphragm for lithium batteries and a preparation method thereof. Background Art

[0002] Lithium batteries are currently widely used in various fields, such as medical electronics, automotive products, and electronic equipment. The ever-expanding application market also places increasingly higher demands on the performance of lithium batteries, among which the most concerned are higher energy density, higher power density, and reliable safety.

[0003] As a key component of the battery, lithium-ion battery separators need to simultaneously assume the functions of electrolyte storage, ion conduction and electrode isolation. Currently, commercial separators are mainly polyolefin materials (such as polyethylene PE and polypropylene PP). Although they have good chemical stability and insulation properties, they have significant defects. First, polyolefin separators have poor thermal stability. The melting points of PE and PP are 135°C and 165°C respectively. They are prone to thermal shrinkage at high temperatures, resulting in internal short circuits in the battery and even safety hazards. Secondly, the non-polar surface of the polyolefin material has low affinity with the electrolyte and poor interfacial wettability, which increases the internal resistance of the battery and affects the rate performance and energy efficiency. In addition, the ionic conductivity of traditional separators is insufficient, which limits the lithium ion transmission rate, resulting in rapid capacity decay and reduced cycle life of the battery at high current density.

[0004] To improve the performance of the diaphragm, existing technologies attempt to introduce organic polymer materials such as polyvinylidene fluoride (PVDF), whose high polarity and chemical stability can enhance the compatibility of the diaphragm with the electrolyte. However, traditional organic polymer slurries rely on organic solvents (such as N-methylpyrrolidone), which have problems such as flammability, toxicity, and environmental pollution. At the same time, it is difficult to balance thermal stability and ion transport efficiency through single polymer modification. In recent years, inorganic ceramic fillers (such as boehmite, γ-AlOOH) have attracted attention due to their high heat resistance, surface hydroxyl activity, and dispersibility, but their composite process and interface bonding with polymers still need to be optimized.

[0005] Therefore, there is an urgent need to develop an environmentally friendly and efficient new composite membrane that can improve the thermal stability of the membrane while improving the electrolyte wettability and ion transport performance through organic-inorganic synergistic modification, thereby meeting the application requirements of high-power and long-life lithium batteries. Summary of the Invention

[0006] To address the problems of poor thermal stability, insufficient electrolyte wettability and low ionic conductivity of existing polyolefin separators, the present invention provides an aqueous organic-inorganic composite separator for lithium batteries and a preparation method thereof. The preparation process is environmentally friendly and can significantly improve the electrochemical performance and safety of lithium batteries.

[0007] The present invention includes the following technical solutions: A water-based organic-inorganic composite membrane for lithium batteries and a preparation method thereof. The water-based organic-inorganic composite membrane for lithium batteries is composited with a polyolefin membrane, an organic polymer, and an inorganic ceramic filler. The membrane comprises a polyolefin base film (such as a PP membrane) and an organic-inorganic composite coating applied to the surface of the polyolefin base film. The composite coating comprises 1% to 80% by weight of the inorganic ceramic filler and an organic polymer as a binder. The membrane is prepared by the following steps: The preparation process of the aqueous organic-inorganic composite membrane for lithium batteries comprises the following steps: adding an organic polymer to deionized water, then adding a certain amount of dispersant and stirring to disperse the mixture; stirring for a period of time until the organic polymer is evenly dispersed, and then adding a certain amount of inorganic ceramic filler. Stirring is continued for a period of time until the slurry is uniformly mixed, and then adding a certain amount of surfactant and stirring to uniformly mix the mixture. The resulting slurry is then ultrasonically disrupted in an ultrasonic disruptor. After completion, the slurry is poured into a petri dish, and a polyolefin membrane is then immersed in the slurry for a period of time. The membrane is then removed and placed in a forced air drying oven for drying. After drying, the organic-inorganic composite membrane is obtained.

[0008] Preferably, the lithium battery uses an aqueous organic-inorganic composite membrane, and the lithium battery is one of a lithium-manganese dioxide battery, a lithium-sulfur dioxide battery, a lithium-iron disulfide battery, a lithium-thionyl chloride battery, a lithium-carbon fluoride battery, a lithium-aluminum fluoride battery, a lithium-sulfur battery, a lithium iron phosphate battery and a ternary lithium battery.

[0009] Preferably, the lithium battery uses an aqueous organic-inorganic composite membrane, and the organic polymer is one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polyethylene oxide, polysiloxane, polyacrylonitrile, and polymethyl methacrylate.

[0010] Preferably, the lithium battery uses an aqueous organic-inorganic composite membrane, and the inorganic ceramic filler is one or more of boehmite, alumina, titanium dioxide, zirconium oxide, silicon dioxide, lithium lanthanum zirconium oxide, lithium lanthanum titanate, lithium aluminum titanium phosphate and lithium aluminum germanium phosphate.

[0011] Preferably, the lithium battery uses a water-based organic-inorganic composite membrane, and the polyolefin membrane is one or more of polyethylene, polypropylene or a composite membrane.

[0012] Preferably, the lithium battery uses a water-based organic-inorganic composite membrane, and the dispersant is one or more of triethyl phosphate, trimethyl phosphate, tributyl phosphate and diethyl phosphate.

[0013] Preferably, the lithium battery uses a water-based organic-inorganic composite diaphragm, and the surfactant is one or more of polydimethylsiloxane, polyether-modified silicone oil and epoxy-modified silicone oil.

[0014] Preferably, for the aqueous organic-inorganic composite membrane used in lithium batteries, the mass ratio of the inorganic ceramic filler to the organic polymer is 1:1 to 1:15. The mass ratio of deionized water to PVDF is 10:1 to 30:1. The volume ratio of deionized water to dispersant is 5:1 to 20:1. The first stirring time is 2 to 12 hours, the second stirring time is 5 to 24 hours, and the third stirring time is 2 to 12 hours. The ultrasonic crushing time is 30 to 240 minutes. The drying temperature in the forced air drying oven is 40 to 100°C, and the drying time is 1 to 20 hours.

[0015] The present invention has the following advantages and positive effects: The present invention prepares an aqueous organic-inorganic composite diaphragm for lithium batteries to improve the performance of lithium batteries. Organic polymers and inorganic ceramic fillers are dissolved in deionized water, and the organic-inorganic composite diaphragm is prepared by a dip-coating method and applied to lithium batteries. The present invention improves the wettability of the diaphragm to the electrolyte by modifying the diaphragm of the lithium battery, thereby increasing the liquid absorption rate of the diaphragm and promoting the transmission of lithium ions. At the same time, the thermal stability of the diaphragm is also improved. The excellent electrochemical performance of the lithium battery under high current density and long-term high-temperature storage conditions is achieved. In addition, the preparation process of the aqueous organic-inorganic composite diaphragm is simple, and the improvement of electrochemical performance and storage performance can be achieved through simple steps, making it easy to achieve large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The scanning electron microscope photo and optical photo of the organic-inorganic composite membrane prepared by the present invention; Figure 2 Schematic diagram of contact angle test between PP membrane, organic-inorganic composite membrane prepared by the present invention and electrolyte; Figure 3 is the ionic conductivity of the PP membrane and the organic-inorganic composite membrane prepared by the present invention; Figure 4 Li / CF3 composite membrane assembled with PP membrane and organic-inorganic composite membrane prepared by the present invention x Rate performance of button cells; Figure 5 Li / CF3 composite membrane assembled with PP membrane and organic-inorganic composite membrane prepared by the present invention x Discharge curves of button cells at 0.1 C rate after storage for 10 to 60 days at room temperature and 55°C. DETAILED DESCRIPTION

[0017] In order to further disclose the content, features and effects of the present invention, the following examples are given and described in detail with reference to the accompanying drawings.

[0018] The present invention provides an aqueous organic-inorganic composite diaphragm for lithium batteries and a preparation method thereof. The organic-inorganic composite diaphragm comprises an organic polymer, an inorganic ceramic filler, and a polyolefin diaphragm. The technical solution is as follows: an organic polymer is added to deionized water and a certain amount of dispersant is added and stirred for a period of time until the organic polymer is evenly dispersed. A certain amount of inorganic ceramic filler is then added thereto, and stirring is continued for a period of time until the slurry is evenly mixed. A certain amount of surfactant is then added thereto and stirring is continued for a period of time, and the resulting slurry is placed in an ultrasonic crusher for ultrasonic crushing. The resulting slurry is poured into a culture dish, a polyolefin diaphragm is placed in the slurry and soaked for a period of time, and then the diaphragm is taken out and placed in a blast drying oven for drying. After drying, an organic-inorganic composite diaphragm is obtained.

[0019] The lithium battery uses a water-based organic-inorganic composite diaphragm, and the lithium battery is one of a lithium-manganese dioxide battery, a lithium-sulfur dioxide battery, a lithium-iron disulfide battery, a lithium-thionyl chloride battery, a lithium-carbon fluoride battery, a lithium-aluminum fluoride battery, a lithium-sulfur battery, a lithium iron phosphate battery and a ternary lithium battery.

[0020] The organic polymer is one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polyethylene oxide, polysiloxane, polyacrylonitrile, and polymethyl methacrylate.

[0021] The inorganic ceramic filler is one or more of boehmite, alumina, titanium dioxide, zirconium oxide, silicon dioxide, lithium lanthanum zirconium oxide, lithium lanthanum titanate, lithium aluminum titanium phosphate and lithium aluminum germanium phosphate.

[0022] The polyolefin diaphragm is one or more of polyethylene, polypropylene and composite diaphragms.

[0023] The dispersant is one or more of triethyl phosphate, trimethyl phosphate, tributyl phosphate and diethyl phosphate.

[0024] The surfactant is one or more of polydimethylsiloxane, polyether modified silicone oil and epoxy modified silicone oil.

[0025] The lithium battery electrolyte is typically a mixture of one or more ester solvents and ether solvents. The ether solvent is a mixture of one or more solvents selected from the group consisting of 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, propylene glycol dimethyl ether, tetrahydrofuran, and ethylene glycol diethyl ether; and the ester solvent is a mixture of one or more solvents selected from the group consisting of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0026] The lithium salt in the electrolyte used in the lithium battery is a mixture of one or more of lithium bis(trifluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium oxalodifluoroborate.

[0027] Example 1: 0.5 g of PVDF was added to 5 mL of deionized water, followed by the addition of 300 μL of triethyl phosphate and stirring. The mixture was stirred for 2 hours until the PVDF was evenly dispersed, and 0.3 g of boehmite particles were added. Stirring was continued for another 2 hours until the slurry was uniformly mixed. 300 μL of polydimethylsiloxane was then added and stirred for 2 hours. The resulting slurry was ultrasonically disrupted in an ultrasonicator for 20 minutes. The resulting slurry was poured into a Petri dish, and a PP separator was immersed in the slurry for 30 minutes. The separator was then removed and dried in a forced air drying oven for 6 hours. After drying, an organic-inorganic (PVDF-boehmite) composite separator was obtained.

[0028] The fluorinated carbon (CF x ), conductive carbon (Super P), and PVDF were ground in a mortar at a mass ratio of 8:1:1 for 30 min, and a certain amount of NMP (N-methylpyrrolidone) was added and stirred for 8 h. The evenly stirred slurry was applied to aluminum foil and dried in a constant temperature vacuum drying oven at 80°C for 8 h. The electrode sheet was punched into a Φ14 mm electrode sheet and placed in a glove box. It was assembled into a button battery with a lithium negative electrode and an organic-inorganic (PVDF-boehmite) composite separator using an ether-based electrolyte for characterization testing.

[0029] The organic-inorganic composite membrane prepared by the present invention was tested and characterized. Figure 1 It can be seen that there is a coating composed of boehmite and PVDF on the surface of the diaphragm, and the surface layer has many micropores. These microporous structures are conducive to the absorption of liquid electrolytes, thereby improving the conductivity of the composite gel polymer electrolyte. Figure 2 As can be seen in (b) of the figure, when the organic-inorganic composite membrane comes into contact with the electrolyte, the electrolyte spreads and penetrates instantly, showing super-lyophilic properties. This is because the surface of boehmite is rich in hydroxyl groups (-OH), which can form a hydrogen bond network with the solvent molecules in the electrolyte, reducing the surface solid-liquid tension. At the same time, the micropores constructed by boehmite and PVDF accelerate the infiltration of the electrolyte through capillary action. The prepared organic-inorganic composite membrane and PP membrane were tested for ionic conductivity, and the test results are shown in the figure below. Figure 3 As shown in (b), the ionic conductivity of the organic-inorganic composite membrane is as high as 1.46 mS cm -1The high ionic conductivity may be caused by these two aspects. The continuous and open pore structure can provide efficient lithium ion transmission channels. The abundant hydroxyl groups (-OH) on the surface of boehmite interact with the polar solvent in the electrolyte through hydrogen bonds, promoting electrolyte infiltration and accelerating Li⁺ transmission. On the other hand, PVDF as a binder not only firmly fixes the boehmite particles on the surface of the base film, but also its amorphous region can be Li + Provide a migration path. The organic-inorganic composite membrane made by the present invention and the original lithium sheet and CF x Positive electrode composition CR2032 type Li / CF x Button cell battery characterization, Figure 4 Li / CF x Discharge curves of the battery at different rates. The discharge specific capacities at 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10.0, and 15.0 C are 940, 855, 825, 780, 705, 603, 590, and 521 mAh / g, respectively. Figure 5 (c) and (d) are Li / CF using organic-inorganic composite membranes provided by embodiments of the present invention. x The discharge curves of button cells at 0.1 C rate after storage for 10 to 60 days at room temperature and 55 ° C are as follows: the discharge capacity after storage for 10, 20, 30 and 60 days at room temperature is 930, 899, 830 and 810 mAh / g, respectively; the discharge capacity after storage for 10, 20, 30 and 60 days at 55 ° C is 910, 879, 800 and 772 mAh / g, respectively. x The battery has a low self-discharge rate and good storage performance. On the one hand, the coating improves the wettability of the diaphragm to the electrolyte, which can store more electrolyte and improve the Li + On the other hand, the coating of the composite diaphragm enhances the thermal stability of the diaphragm and can inhibit the shrinkage and deformation of the diaphragm at high temperatures.

[0030] Comparative Example: The original PP separator without modification was used, and the rest was exactly the same as in the example, and a CR2032 type Li / CF x Button battery.

[0031] The unmodified original PP separator and the CR2032 type Li / CF x Button battery test: Figure 2 (a) shows the contact angle between the original PP separator and the electrolyte is 36.3°. The wettability of the PP separator to the electrolyte is much lower than that of the organic-inorganic composite separator. Figure 3As shown in (b), the ionic conductivity of the original PP separator is 0.42 mScm -1 , which is lower than the ionic conductivity of the organic-inorganic composite membrane. Figure 4 (a) is a Li / CF assembled using a PP separator x The discharge curves of the button battery at different rates show that the discharge specific capacities at 0.1, 0.2, 0.5, 1.0, 2.0, and 5.0 C are 856, 818, 744, 662, 522, and 435 mAh / g, respectively, which are much lower than those of the Li / CF prepared using the organic-inorganic composite membrane provided in Example 1. x Button battery. Figure 5 (a) and (b) are Li / CF assembled using PP separators. x The discharge curves of the button cell at 0.1 C rate after storage for 10 to 60 days at room temperature and 55°C are as follows: the discharge specific capacities after storage for 10, 20, 30, and 60 days at room temperature are 849, 820, 797, and 771 mAh / g, respectively; and the discharge specific capacities after storage for 10, 20, 30, and 60 days at 55°C are 799, 753, 688, and 271 mAh / g, respectively. Its storage performance is far inferior to that of the Li / CF prepared using the organic-inorganic composite membrane provided in Example 1. x Button battery.

[0032] Example 2: 0.5 g of PVDF was added to 5 mL of deionized water, and then 300 μL of C6H 15 The mixture was stirred with O4P for 2 h until the PVDF was evenly dispersed. 0.1 g of boehmite particles were then added. Stirring was continued for another 2 h until the slurry was uniformly mixed. 300 μL of polydimethylsiloxane was then added and stirred for 2 h. The resulting slurry was ultrasonically disrupted in an ultrasonicator for 20 min. The resulting slurry was poured into a Petri dish, and a PP separator was immersed in the slurry for 30 min. The separator was then removed and dried in a forced air drying oven for 6 h. After drying, an organic-inorganic (PVDF-boehmite) composite separator was obtained.

[0033] Completely the same as in Example 1, CR2032 type Li / CF x Button battery.

[0034] Example 3 0.5 g of PVDF was added to 5 mL of deionized water, followed by the addition of 300 μL of triethyl phosphate and stirring. The mixture was stirred for 2 hours until the PVDF was evenly dispersed, and 0.2 g of boehmite particles were added. Stirring was continued for another 2 hours until the slurry was uniformly mixed. 300 μL of polydimethylsiloxane was then added and stirred for 2 hours. The resulting slurry was ultrasonically disrupted in an ultrasonicator for 20 minutes. The resulting slurry was poured into a Petri dish, and a PP separator was immersed in the slurry for 30 minutes. The separator was then removed and dried in a forced air drying oven for 6 hours. After drying, an organic-inorganic (PVDF-boehmite) composite separator was obtained.

[0035] Completely the same as in Example 1, CR2032 type Li / CF x Button battery.

[0036] Example 4 0.5 g of PVDF was added to 5 mL of deionized water, followed by the addition of 300 μL of triethyl phosphate and stirring. The mixture was stirred for 2 hours until the PVDF was evenly dispersed, and 0.3 g of alumina particles were added. Stirring was continued for another 2 hours until the slurry was uniformly mixed. 300 μL of polydimethylsiloxane was added and stirred for 2 hours. The resulting slurry was ultrasonically disrupted in an ultrasonicator for 20 minutes. The resulting slurry was poured into a Petri dish, and a PP separator was immersed in the slurry for 30 minutes. The separator was then removed and dried in a forced air drying oven for 6 hours. After drying, an organic-inorganic (PVDF-alumina) composite separator was obtained.

[0037] Completely the same as in Example 1, CR2032 type Li / CF x Button battery.

[0038] Although preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above-described specific embodiments. The above-described specific embodiments are merely adaptable and not restrictive. Those skilled in the art, guided by the present invention, may devise various embodiments without departing from the spirit of the present invention and the scope of protection of the claims. All such embodiments fall within the scope of protection of the present invention.

Claims

1. A water-based organic-inorganic composite diaphragm for lithium batteries and a preparation method thereof, characterized in that: The aqueous organic-inorganic composite membrane for lithium batteries is composed of a polyolefin membrane, an organic polymer, and an inorganic ceramic filler, that is, a polyolefin membrane and an organic-inorganic composite coating coated on the surface thereof; in the organic-inorganic composite coating, the inorganic ceramic filler accounts for 1% to 80% by mass, and the organic polymer serves as a binder. Specifically: The preparation process of the aqueous organic-inorganic composite membrane for lithium batteries is as follows: adding an organic polymer to deionized water, then adding a certain amount of dispersant thereto for stirring and dispersing; stirring for a period of time until the organic polymer is evenly dispersed, then adding a certain amount of inorganic ceramic filler thereto; continuing to stir for a period of time until the slurry is evenly mixed, adding a certain amount of surfactant thereto for stirring evenly, and placing the obtained slurry into an ultrasonic crusher for ultrasonic crushing; after completion, pouring the slurry into a culture dish, then placing a polyolefin membrane into the slurry and soaking it for a period of time, then taking out the membrane and placing it in a blast drying oven for drying, and after drying, obtaining the organic-inorganic composite membrane.

2. The aqueous organic-inorganic composite diaphragm for lithium batteries and the preparation method thereof according to claim 1, characterized in that: The lithium battery is one of a lithium-manganese dioxide battery, a lithium-sulfur dioxide battery, a lithium-iron disulfide battery, a lithium-thionyl chloride battery, a lithium-carbon fluoride battery, a lithium-aluminum fluoride battery, a lithium-sulfur battery, a lithium iron phosphate battery and a ternary lithium battery.

3. The aqueous organic-inorganic composite diaphragm for lithium batteries and the preparation method thereof according to claim 1, characterized in that: The organic polymer is one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polyethylene oxide, polysiloxane, polyacrylonitrile, and polymethyl methacrylate.

4. The aqueous organic-inorganic composite membrane for lithium batteries and the preparation method thereof according to claim 1, characterized in that: The inorganic ceramic filler is one or more of boehmite, alumina, titanium dioxide, zirconium oxide, silicon dioxide, lithium lanthanum zirconium oxide, lithium lanthanum titanate, lithium aluminum titanium phosphate and lithium aluminum germanium phosphate.

5. The aqueous organic-inorganic composite diaphragm for lithium batteries and the preparation method thereof according to claim 1, characterized in that: The polyolefin diaphragm is one or more of a polyethylene diaphragm, a polypropylene diaphragm or a composite diaphragm.

6. The aqueous organic-inorganic composite diaphragm for lithium batteries and the preparation method thereof according to claim 1, characterized in that: The dispersant is one or more of triethyl phosphate, trimethyl phosphate, tributyl phosphate and diethyl phosphate.

7. The aqueous organic-inorganic composite diaphragm for lithium batteries and the preparation method thereof according to claim 1, characterized in that: The surfactant is one or more of polydimethylsiloxane, polyether modified silicone oil and epoxy modified silicone oil.

8. The aqueous organic-inorganic composite diaphragm for lithium batteries and the preparation method thereof according to claim 1, characterized in that: The mass ratio of the inorganic ceramic filler to the organic polymer is 1:1 to 1:15; the mass ratio of the deionized water to the PVDF is 10:1 to 30:1; the volume ratio of the deionized water to the dispersant is 5:1 to 20:1; the first stirring time is 2 to 12 hours, the second stirring time is 5 to 24 hours, and the third stirring time is 2 to 12 hours; the ultrasonic crushing time is 30 to 240 minutes; the drying temperature in the blast drying oven is 40 to 100°C; and the drying time is 1 to 20 hours.

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